diff --git a/problems/0039.组合总和.md b/problems/0039.组合总和.md
index 37d5614e..81558cc1 100644
--- a/problems/0039.组合总和.md
+++ b/problems/0039.组合总和.md
@@ -598,6 +598,66 @@ object Solution {
   }
 }
 ```
+### C#
+```csharp
+public class Solution
+{
+    public IList<IList<int>> res = new List<IList<int>>();
+    public IList<int> path = new List<int>();
+    public IList<IList<int>> CombinationSum(int[] candidates, int target)
+    {
+        BackTracking(candidates, target, 0, 0);
+        return res;
+    }
+    public void BackTracking(int[] candidates, int target, int start, int sum)
+    {
+        if (sum > target) return;
+        if (sum == target)
+        {
+            res.Add(new List<int>(path));
+            return;
+        }
+        for (int i = start; i < candidates.Length; i++)
+        {
+            sum += candidates[i];
+            path.Add(candidates[i]);
+            BackTracking(candidates, target, i, sum);
+            sum -= candidates[i];
+            path.RemoveAt(path.Count - 1);
+        }
+    }
+}
+
+// 剪枝优化
+public class Solution
+{
+    public IList<IList<int>> res = new List<IList<int>>();
+    public IList<int> path = new List<int>();
+    public IList<IList<int>> CombinationSum(int[] candidates, int target)
+    {
+        Array.Sort(candidates);
+        BackTracking(candidates, target, 0, 0);
+        return res;
+    }
+    public void BackTracking(int[] candidates, int target, int start, int sum)
+    {
+        if (sum > target) return;
+        if (sum == target)
+        {
+            res.Add(new List<int>(path));
+            return;
+        }
+        for (int i = start; i < candidates.Length && sum + candidates[i] <= target; i++)
+        {
+            sum += candidates[i];
+            path.Add(candidates[i]);
+            BackTracking(candidates, target, i, sum);
+            sum -= candidates[i];
+            path.RemoveAt(path.Count - 1);
+        }
+    }
+}
+```
 
 
 <p align="center">