diff --git a/.idea/workspace.xml b/.idea/workspace.xml
index 450c4c0..3ffb7d5 100644
--- a/.idea/workspace.xml
+++ b/.idea/workspace.xml
@@ -2,6 +2,8 @@
 <project version="4">
   <component name="ChangeListManager">
     <list default="true" id="be5bf74e-ad1c-4197-8a1f-ac93566d8aa7" name="Default" comment="init">
+      <change type="MODIFICATION" beforePath="$PROJECT_DIR$/README.md" afterPath="$PROJECT_DIR$/README.md" />
+      <change type="MODIFICATION" beforePath="$PROJECT_DIR$/机器学习/集成学习/GBDT.md" afterPath="$PROJECT_DIR$/机器学习/集成学习/GBDT.md" />
       <change type="MODIFICATION" beforePath="$PROJECT_DIR$/机器学习/集成学习/Xgboost.md" afterPath="$PROJECT_DIR$/机器学习/集成学习/Xgboost.md" />
     </list>
     <ignored path="Reflection_Summary.iws" />
@@ -23,7 +25,7 @@
   </component>
   <component name="FileEditorManager">
     <leaf SIDE_TABS_SIZE_LIMIT_KEY="300">
-      <file leaf-file-name="README.md" pinned="false" current-in-tab="false">
+      <file leaf-file-name="README.md" pinned="false" current-in-tab="true">
         <entry file="file://$PROJECT_DIR$/README.md">
           <provider editor-type-id="split-provider[text-editor;markdown-preview-editor]">
             <state split_layout="SPLIT">
@@ -36,8 +38,8 @@
           </provider>
           <provider selected="true" editor-type-id="split-provider[text-editor;MarkdownPreviewEditor]">
             <state split_layout="SPLIT">
-              <first_editor relative-caret-position="355">
-                <caret line="241" column="25" selection-start-line="241" selection-start-column="25" selection-end-line="241" selection-end-column="25" />
+              <first_editor relative-caret-position="385">
+                <caret line="243" column="26" selection-start-line="243" selection-start-column="26" selection-end-line="243" selection-end-column="26" />
                 <folding />
               </first_editor>
               <second_editor>
@@ -51,8 +53,8 @@
         <entry file="file://$PROJECT_DIR$/机器学习/集成学习/GBDT.md">
           <provider selected="true" editor-type-id="split-provider[text-editor;markdown-preview-editor]">
             <state split_layout="SPLIT">
-              <first_editor relative-caret-position="390">
-                <caret line="75" column="0" selection-start-line="75" selection-start-column="0" selection-end-line="78" selection-end-column="23" />
+              <first_editor relative-caret-position="520">
+                <caret line="109" column="0" selection-start-line="109" selection-start-column="0" selection-end-line="109" selection-end-column="0" />
                 <folding />
               </first_editor>
               <second_editor />
@@ -71,12 +73,12 @@
           </provider>
         </entry>
       </file>
-      <file leaf-file-name="Xgboost.md" pinned="false" current-in-tab="true">
+      <file leaf-file-name="Xgboost.md" pinned="false" current-in-tab="false">
         <entry file="file://$PROJECT_DIR$/机器学习/集成学习/Xgboost.md">
           <provider selected="true" editor-type-id="split-provider[text-editor;markdown-preview-editor]">
             <state split_layout="SPLIT">
-              <first_editor relative-caret-position="345">
-                <caret line="23" column="13" selection-start-line="23" selection-start-column="13" selection-end-line="23" selection-end-column="13" />
+              <first_editor relative-caret-position="430">
+                <caret line="72" column="21" selection-start-line="72" selection-start-column="2" selection-end-line="72" selection-end-column="21" />
                 <folding />
               </first_editor>
               <second_editor />
@@ -138,8 +140,8 @@
         <option value="$PROJECT_DIR$/机器学习/支持向量机/支持向量机.md" />
         <option value="$PROJECT_DIR$/数据预处理/特征提取/数据变换.md" />
         <option value="$PROJECT_DIR$/机器学习/集成学习/GBDT.md" />
-        <option value="$PROJECT_DIR$/README.md" />
         <option value="$PROJECT_DIR$/机器学习/集成学习/Xgboost.md" />
+        <option value="$PROJECT_DIR$/README.md" />
       </list>
     </option>
   </component>
@@ -1409,20 +1411,20 @@
         </state>
       </provider>
     </entry>
-    <entry file="file://$PROJECT_DIR$/README.md">
-      <provider editor-type-id="split-provider[text-editor;markdown-preview-editor]">
+    <entry file="file://$PROJECT_DIR$/机器学习/集成学习/Xgboost.md">
+      <provider selected="true" editor-type-id="split-provider[text-editor;markdown-preview-editor]">
         <state split_layout="SPLIT">
-          <first_editor relative-caret-position="0">
-            <caret line="0" column="0" selection-start-line="0" selection-start-column="0" selection-end-line="0" selection-end-column="0" />
+          <first_editor relative-caret-position="430">
+            <caret line="72" column="21" selection-start-line="72" selection-start-column="2" selection-end-line="72" selection-end-column="21" />
             <folding />
           </first_editor>
           <second_editor />
         </state>
       </provider>
-      <provider selected="true" editor-type-id="split-provider[text-editor;MarkdownPreviewEditor]">
+      <provider editor-type-id="split-provider[text-editor;MarkdownPreviewEditor]">
         <state split_layout="SPLIT">
-          <first_editor relative-caret-position="355">
-            <caret line="241" column="25" selection-start-line="241" selection-start-column="25" selection-end-line="241" selection-end-column="25" />
+          <first_editor relative-caret-position="0">
+            <caret line="0" column="0" selection-start-line="0" selection-start-column="0" selection-end-line="0" selection-end-column="0" />
             <folding />
           </first_editor>
           <second_editor>
@@ -1434,8 +1436,8 @@
     <entry file="file://$PROJECT_DIR$/机器学习/集成学习/GBDT.md">
       <provider selected="true" editor-type-id="split-provider[text-editor;markdown-preview-editor]">
         <state split_layout="SPLIT">
-          <first_editor relative-caret-position="390">
-            <caret line="75" column="0" selection-start-line="75" selection-start-column="0" selection-end-line="78" selection-end-column="23" />
+          <first_editor relative-caret-position="520">
+            <caret line="109" column="0" selection-start-line="109" selection-start-column="0" selection-end-line="109" selection-end-column="0" />
             <folding />
           </first_editor>
           <second_editor />
@@ -1453,20 +1455,20 @@
         </state>
       </provider>
     </entry>
-    <entry file="file://$PROJECT_DIR$/机器学习/集成学习/Xgboost.md">
-      <provider selected="true" editor-type-id="split-provider[text-editor;markdown-preview-editor]">
+    <entry file="file://$PROJECT_DIR$/README.md">
+      <provider editor-type-id="split-provider[text-editor;markdown-preview-editor]">
         <state split_layout="SPLIT">
-          <first_editor relative-caret-position="345">
-            <caret line="23" column="13" selection-start-line="23" selection-start-column="13" selection-end-line="23" selection-end-column="13" />
+          <first_editor relative-caret-position="0">
+            <caret line="0" column="0" selection-start-line="0" selection-start-column="0" selection-end-line="0" selection-end-column="0" />
             <folding />
           </first_editor>
           <second_editor />
         </state>
       </provider>
-      <provider editor-type-id="split-provider[text-editor;MarkdownPreviewEditor]">
+      <provider selected="true" editor-type-id="split-provider[text-editor;MarkdownPreviewEditor]">
         <state split_layout="SPLIT">
-          <first_editor relative-caret-position="0">
-            <caret line="0" column="0" selection-start-line="0" selection-start-column="0" selection-end-line="0" selection-end-column="0" />
+          <first_editor relative-caret-position="385">
+            <caret line="243" column="26" selection-start-line="243" selection-start-column="26" selection-end-line="243" selection-end-column="26" />
             <folding />
           </first_editor>
           <second_editor>
diff --git a/README.md b/README.md
index 391382a..3a9452b 100644
--- a/README.md
+++ b/README.md
@@ -240,6 +240,8 @@
     - [xgboost如何处理缺失值](机器学习/集成学习/Xgboost.md#L164)
     - [xgboost在计算速度上有了哪些点上提升](机器学习/集成学习/Xgboost.md#L164)
     - [xgboost特征重要性是如何得到的](机器学习/集成学习/Xgboost.md#L164)
+    - [XGBoost中如何对树进行剪枝](机器学习/集成学习/Xgboost.md#L164)
+    - [XGBoost模型如果过拟合了怎么解决](机器学习/集成学习/Xgboost.md#L164)
 - FM/FFM
 - SVM
     - [简单介绍SVM](机器学习/支持向量机/支持向量机.md#L164)
diff --git "a/\346\234\272\345\231\250\345\255\246\344\271\240/\351\233\206\346\210\220\345\255\246\344\271\240/GBDT.md" "b/\346\234\272\345\231\250\345\255\246\344\271\240/\351\233\206\346\210\220\345\255\246\344\271\240/GBDT.md"
index 7d89fde..7c97d22 100644
--- "a/\346\234\272\345\231\250\345\255\246\344\271\240/\351\233\206\346\210\220\345\255\246\344\271\240/GBDT.md"
+++ "b/\346\234\272\345\231\250\345\255\246\344\271\240/\351\233\206\346\210\220\345\255\246\344\271\240/GBDT.md"
@@ -98,6 +98,7 @@ Cart tree，但是都是回归树
 - 相同：
     - 都是多棵树的组合
 - 不同：
+    - RF每次迭代的样本是从全部训练集中有放回抽样形成的，而GBDT每次使用全部样本
     - gbdt对异常值比rf更加敏感
     - gbdt是串行，rf是并行
     - gbdt是cart回归树，rf是cart分类回归树都可以
@@ -105,4 +106,5 @@ Cart tree，但是都是回归树
     - gbdt对输出值是进行加权求和，rf对输出值是进行投票或者平均
     
 # GBDT和LR的差异？
-从决策边界来说，线性回归的决策边界是一条直线，逻辑回归的决策边界是一条曲线，而GBDT的决策边界可能是很多条线
\ No newline at end of file
+- 从决策边界来说，线性回归的决策边界是一条直线，逻辑回归的决策边界是一条曲线，而GBDT的决策边界可能是很多条线
+- 当在高维稀疏特征的场景下，LR的效果一般会比GBDT好。因为LR有参数惩罚，GBDT容易造成过拟合
\ No newline at end of file
diff --git "a/\346\234\272\345\231\250\345\255\246\344\271\240/\351\233\206\346\210\220\345\255\246\344\271\240/Xgboost.md" "b/\346\234\272\345\231\250\345\255\246\344\271\240/\351\233\206\346\210\220\345\255\246\344\271\240/Xgboost.md"
index 24c28c0..d1891ca 100644
--- "a/\346\234\272\345\231\250\345\255\246\344\271\240/\351\233\206\346\210\220\345\255\246\344\271\240/Xgboost.md"
+++ "b/\346\234\272\345\231\250\345\255\246\344\271\240/\351\233\206\346\210\220\345\255\246\344\271\240/Xgboost.md"
@@ -62,4 +62,18 @@ MAPE:![](https://tva1.sinaimg.cn/large/006y8mN6gy1g94mx7uyuej303f0170sj.jpg)
 # xgboost特征重要性是如何得到的？
 - ’weight‘：代表着某个特征被选作分裂结点的次数；
 - ’gain‘：使用该特征作为分类结点的信息增益；
-- ’cover‘：某特征作为划分结点，覆盖样本总数的平均值；
\ No newline at end of file
+- ’cover‘：某特征作为划分结点，覆盖样本总数的平均值；
+
+# XGBoost中如何对树进行剪枝？
+- 在目标函数中增加了正则项：叶子结点树+叶子结点权重的L2模的平方
+- 在结点分裂时，定义了一个阈值，如果分裂后目标函数的增益小于该阈值，则不分裂
+- 当引入一次分裂后，重新计算新生成的左、右两个叶子结点的样本权重和。如果任一个叶子结点的样本权重低于某一个阈值（最小样本权重和），也会放弃此次分裂
+- XGBoost 先从顶到底建立树直到最大深度，再从底到顶反向检查是否有不满足分裂条件的结点，进行剪枝
+
+# XGBoost模型如果过拟合了怎么解决？
+- 直接修改模型：
+    - 降低树的深度
+    - 增大叶子结点的权重
+    - 增大惩罚系数
+- subsample的力度变大，降低异常点的影响
+- 减小learning rate，提高estimator
\ No newline at end of file