diff --git a/include/tree.h b/include/tree.h
index 79c0491..9d213b6 100644
--- a/include/tree.h
+++ b/include/tree.h
@@ -104,8 +104,8 @@ struct _tree
     bool (*delete)(struct _tree* self, void* obj);
 
     struct _tree_node* (*find)(struct _tree* self, void* obj);
-    struct _tree_node* (*find_min)(struct _tree* self);
-    struct _tree_node* (*find_max)(struct _tree* self);
+    struct _tree_node* (*find_min)(struct _tree* self, struct _tree_node* root);
+    struct _tree_node* (*find_max)(struct _tree* self, struct _tree_node* root);
 
     bool (*rebalance)(struct _tree* self, struct _tree_node* root);
     uint32_t (*height)(struct _tree* self, struct _tree_node* root);
diff --git a/src/tree.c b/src/tree.c
index ccec59f..d249c7e 100644
--- a/src/tree.c
+++ b/src/tree.c
@@ -1695,41 +1695,72 @@ bool tree_avl_insert(struct _tree* self, void* obj)
     return true;
 }
 
+static bool tree_avl_delete_single_child(struct _tree* self, struct _tree_node* node)
+{
+    assert(self != NULL);
+    assert(node != NULL);
+
+    if(node->parent == NULL)
+    {
+        self->_root = node->left != NULL ? node->left : node->right;
+    }
+    else
+    {
+        if(node->parent->left == node)
+        {
+            node->left->parent = node->parent;
+            node->parent->left = node->left != NULL ? node->left : node->right;
+        }
+        else if(node->parent->right == node)
+        {
+            node->right->parent = node->parent;
+            node->parent->right = node->left != NULL ? node->left : node->right;
+        }
+    }
+    return true;
+}
+
+static bool tree_avl_delete_double_child(struct _tree* self, struct _tree_node* node)
+{
+    assert(self != NULL);
+    assert(node != NULL);
+    struct _tree_node* tmp = self->find_min(self, node->right);
+    if(tmp == NULL)
+    {
+        return false;
+    }
+    memmove(node->obj, tmp->obj, self->_obj_size);
+    tree_avl_delete_single_child(self, tmp);
+    return true;
+}
+
 bool tree_avl_delete(struct _tree* self, void* obj)
 {
     assert(self != NULL);
     assert(obj != NULL);
     assert(self->compare != NULL);
 
-    // if 
     if(self->empty(self))
     {
         return false;
     }
-    else
+
+    struct _tree_node* node = self->find(self, obj);
+    if(node == NULL)
     {
-        struct _tree_node* node = self->find(self, obj);
-        if(node == NULL)
-        {
-            return false;
-        }
-
-        if(obj != NULL)
-        {
-            memmove(obj, node->obj, self->_obj_size);
-        }
-
-        if(node->parent->left == node)
-        {
-            node->parent->left = NULL;
-        }
-        else if(node->parent->right == node)
-        {
-
-        }
-        tree_node_free(node);
+        return false;
     }
 
+    if(node->left != NULL && node->right != NULL)
+    {
+        tree_avl_delete_double_child(self, node);
+    }
+    else
+    {
+        tree_avl_delete_single_child(self, node);
+    }
+
+    tree_node_free(node);
     self->_size--;
     return true;
 }
@@ -1917,6 +1948,28 @@ void tree_avl_breadth(struct _tree* self, struct _tree_node* root)
     queue_free(queue);
 }
 
+static struct _tree_node* tree_find_min(struct _tree* self, struct _tree_node* root)
+{
+    assert(self != NULL);
+    assert(root != NULL);
+    if(root->left == NULL)
+    {
+        return root;
+    }
+    return tree_find_min(self, root->left);
+}
+
+static struct _tree_node* tree_find_max(struct _tree* self, struct _tree_node* root)
+{
+    assert(self != NULL);
+    assert(root != NULL);
+    if(root->right == NULL)
+    {
+        return root;
+    }
+    return tree_find_max(self, root->right);
+}
+
 bool tree_avl_init(struct _tree *self, uint32_t obj_size)
 {
     assert(self != NULL);
@@ -1942,6 +1995,8 @@ bool tree_avl_init(struct _tree *self, uint32_t obj_size)
     self->find = tree_avl_find;
     self->height = tree_height;
     self->rebalance = tree_avl_rebalance;
+    self->find_max = tree_find_max;
+    self->find_min = tree_find_min;
 
     self->_root = NULL;
 
diff --git a/test/test.c b/test/test.c
index 2b4e99f..481f41c 100644
--- a/test/test.c
+++ b/test/test.c
@@ -10,10 +10,13 @@ int compare_num(void *obj, void *obj2)
 {
     int num1 = *(int*)obj;
     int num2 = *(int*)obj2;
-    return num1 - num2 > 0 ? 1 : -1;
+    if(num1 == num2)
+    {
+        return 0;
+    }
+    return num1 > num2 ? 1 : -1;
 }
 
-
 void print_struct(void* obj)
 {
     struct _student* student = (struct _student*)obj;
diff --git a/test/tree_test.c b/test/tree_test.c
index 78014c6..e17cc52 100644
--- a/test/tree_test.c
+++ b/test/tree_test.c
@@ -331,17 +331,26 @@ void test_tree_num(void)
     tree->breadth(tree, tree->_root);
     printf("\n");
 
-#if 0
-    while(!tree->empty(tree))
+    for (i = 0; i < len; i++)
     {
+        temp = data[i];
         tree->delete(tree, &temp);
 
-        printf("pop = ");
+        printf("delete = ");
         tree->print_obj(&temp);
 
         printf("size = %2d\n", tree->size(tree));
+
+        printf("----- breadth -----\n");
+        tree->breadth(tree, tree->_root);
+        printf("\n");
     }
-#endif
+
+    if(tree->empty(tree))
+    {
+        printf("----- empty -----\n");
+    }
+
     tree_free(tree);
 }