diff --git a/SunnyUI/Controls/DropItem/UIComboTreeViewItem.cs b/SunnyUI/Controls/DropItem/UIComboTreeViewItem.cs
index 4274a98c..7278ff95 100644
--- a/SunnyUI/Controls/DropItem/UIComboTreeViewItem.cs
+++ b/SunnyUI/Controls/DropItem/UIComboTreeViewItem.cs
@@ -1,5 +1,4 @@
 using System.ComponentModel;
-using System.Windows.Forms;
 
 namespace Sunny.UI
 {
@@ -207,23 +206,10 @@ namespace Sunny.UI
 
         private void uiCheckBox1_CheckedChanged(object sender, System.EventArgs e)
         {
-            foreach (TreeNode node in treeView.Nodes)
-            {
-                CheckAllChildNodes(node, uiCheckBox1.Checked);
-            }
-        }
-
-        public void CheckAllChildNodes(TreeNode treeNode, bool nodeChecked)
-        {
-            treeNode.Checked = nodeChecked;
-            foreach (TreeNode node in treeNode.Nodes)
-            {
-                node.Checked = nodeChecked;
-                if (node.Nodes.Count > 0)
-                {
-                    CheckAllChildNodes(node, nodeChecked);
-                }
-            }
+            if (uiCheckBox1.Checked)
+                treeView.CheckedAll();
+            else
+                treeView.UnCheckedAll();
         }
     }
 }
diff --git a/SunnyUI/Controls/DropItem/UIDropControl.cs b/SunnyUI/Controls/DropItem/UIDropControl.cs
index 1efeec03..edb148a8 100644
--- a/SunnyUI/Controls/DropItem/UIDropControl.cs
+++ b/SunnyUI/Controls/DropItem/UIDropControl.cs
@@ -566,7 +566,6 @@ namespace Sunny.UI
 
                 DropDown?.Invoke(this, e);
 
-
                 if (fullControlSelect || MouseLocation.X > Width - 30)
                 {
                     ButtonClick?.Invoke(this, e);
diff --git a/SunnyUI/Controls/UIComboTreeView.cs b/SunnyUI/Controls/UIComboTreeView.cs
index 28cc71a1..f3b61071 100644
--- a/SunnyUI/Controls/UIComboTreeView.cs
+++ b/SunnyUI/Controls/UIComboTreeView.cs
@@ -24,6 +24,7 @@
  * 2022-11-30: V3.3.0 增加Clear方法
  * 2023-02-04: V3.3.1 下拉框增加显示全选选择框
  * 2023-04-02: V3.3.4 显示清除按钮
+ * 2023-06-12: V3.3.8 修复使用清空按钮后，再次打开下拉框，上次的选择内容还是存在
 ******************************************************************************/
 
 using System;
@@ -229,6 +230,7 @@ namespace Sunny.UI
                 NeedDrawClearButton = false;
                 Text = "";
                 TreeView.SelectedNode = null;
+                TreeView.UnCheckedAll();
                 Invalidate();
                 return;
             }
diff --git a/SunnyUI/Controls/UITreeView.cs b/SunnyUI/Controls/UITreeView.cs
index af0b0fa5..fa9a5d11 100644
--- a/SunnyUI/Controls/UITreeView.cs
+++ b/SunnyUI/Controls/UITreeView.cs
@@ -94,6 +94,16 @@ namespace Sunny.UI
             view.MouseClick += View_MouseClick;
         }
 
+        public void CheckedAll()
+        {
+            view.CheckedAll();
+        }
+
+        public void UnCheckedAll()
+        {
+            view.UnCheckedAll();
+        }
+
         protected override void Dispose(bool disposing)
         {
             base.Dispose(disposing);
@@ -1341,6 +1351,24 @@ namespace Sunny.UI
                     }
                 }
             }
+
+            public void CheckedAll()
+            {
+                foreach (TreeNode node in Nodes)
+                {
+                    node.Checked = true;
+                    SetChildNodeCheckedState(node, true);
+                }
+            }
+
+            public void UnCheckedAll()
+            {
+                foreach (TreeNode node in Nodes)
+                {
+                    node.Checked = false;
+                    SetChildNodeCheckedState(node, false);
+                }
+            }
         }
     }
 }
\ No newline at end of file