diff --git a/lib/add.js b/lib/add.js
index 1714b95..1bbb725 100644
--- a/lib/add.js
+++ b/lib/add.js
@@ -1,5 +1,18 @@
-function add() {
-  // 实现该函数
+function add(a, b) {
+  const maxLength = Math.max(a.length, b.length);
+  const num1 = a.padStart(maxLength, '0');
+  const num2 = b.padStart(maxLength, '0');
+  let res = '';
+  let carry = 0;
+  for (let i = num1.length - 1; i >= 0; --i) {
+    const count = parseInt(num1[i]) + parseInt(num2[i]) + carry;
+    carry = Math.floor(count / 10);
+    res = count % 10 + res;
+  }
+  if (carry) {
+    res = '1' + res;
+  }
+  return res;
 }
 
 module.exports = add
\ No newline at end of file