diff --git a/lib/add.js b/lib/add.js
index 1714b95..bb252ac 100644
--- a/lib/add.js
+++ b/lib/add.js
@@ -1,5 +1,20 @@
-function add() {
-  // 实现该函数
+// 实现大数相加
+function add(num1, num2) {
+  const num1Arr = num1.split('').reverse();
+  const num2Arr = num2.split('').reverse();
+  const result = [];
+  let carry = 0;
+  let len = Math.max(num1Arr.length, num2Arr.length);
+  for (let i = 0; i < len; i++) {
+    const sum = Number(num1Arr[i]) + Number(num2Arr[i]) + carry;
+    carry = Math.floor(sum / 10);
+    result.push(sum % 10);
+  }
+  if (carry) {
+    result.push(carry);
+  }
+  return result.reverse().join('');
+
 }
 
 module.exports = add
\ No newline at end of file