diff --git a/src/heap.c b/src/heap.c
index 490e159..124cd1e 100644
--- a/src/heap.c
+++ b/src/heap.c
@@ -30,6 +30,7 @@ static int parent(int i)
 bool heap_peek(struct _heap* self, void* obj)
 {
     assert(self != NULL);
+    assert(obj != NULL);
     if(obj == NULL)
     {
         return false;
@@ -52,13 +53,14 @@ static void heap_swap(struct _heap* self, int i, int j)
     memmove(self->obj + j * self->_obj_size, tmp, self->_obj_size);
 }
 
-static void heap_fixed(struct _heap* self, int i)
+static void heap_fixed_up(struct _heap* self, int i)
 {
     assert(self != NULL);
     int p = 0;
     while(1)
     {
         p = parent(i);
+        // 若当前节点大于其父节点，则交换位置，否则退出循环
         if(p < 0 || self->compare(self->obj + i * self->_obj_size, self->obj + p * self->_obj_size) <= 0)
         {
             break;
@@ -79,7 +81,37 @@ bool heap_push(struct _heap* self, void* obj)
     memmove(self->obj + index * self->_obj_size, obj, self->_obj_size);
     self->_size++;
 
-    heap_fixed(self, index);
+    heap_fixed_up(self, index);
+}
+
+static void heap_fixed_down(struct _heap* self, int i)
+{
+    assert(self != NULL);
+    int l = 0,r = 0;
+    int max = 0;
+
+    while(1)
+    {
+        l = left(i);
+        r = right(i);
+        max = i;
+
+        if(l < self->size(self) && self->compare(self->obj + l * self->_obj_size, self->obj + max * self->_obj_size) > 0)
+        {
+            max = l;
+        }
+
+        if(r < self->size(self) && self->compare(self->obj + r * self->_obj_size, self->obj + max * self->_obj_size) > 0)
+        {
+            max = r;
+        }
+        if(max == i)
+        {
+            break;
+        }
+        heap_swap(self, i, max);
+        i = max;
+    }
 }
 
 bool heap_pop(struct _heap* self, void* obj)
@@ -89,13 +121,15 @@ bool heap_pop(struct _heap* self, void* obj)
     {
         return false;
     }
-    heap_swap(self, 0, self->size(self) - 1);
+    int index = self->size(self) - 1;
+    heap_swap(self, 0, index);
     if(obj != NULL)
     {
-        memmove(obj, self->obj, self->_obj_size);
+        memmove(obj, self->obj + index * self->_obj_size, self->_obj_size);
     }
     self->_size--;
-    heap_fixed(self, 0);
+    heap_fixed_down(self, 0);
+    return true;
 }
 
 void heap_setmin(struct _heap* self, bool min_flag)
@@ -141,7 +175,7 @@ void heap_print(struct _heap* self)
     void* obj = NULL;
     uint32_t offset = 0;
 
-    for (int i = self->size(self) - 1; i >= 0; i--)
+    for (int i = 0; i < self->size(self); i++)
     {
         offset = self->_obj_size * i;
         obj = (char *)self->obj + offset;
diff --git a/test/test_heap.c b/test/test_heap.c
index 9b4cce5..dc81fe3 100644
--- a/test/test_heap.c
+++ b/test/test_heap.c
@@ -13,10 +13,10 @@
 void test_heap_num(void)
 {
     uint32_t i = 0;
-    int data[] = { 2,1,3,4};
+    // int data[] = { 2,1,3,4};
     // int data[] = { 1,2,3,4,5,6};
     // int data[] = { 5,2,3,1,7,8,6 };
-    // int data[] = { 5,2,3,1,7,8,6,4,9,10,12,11,15,14,13 };
+    int data[] = { 5,2,3,1,7,8,6,4,9,10,12,11,15,14,13 };
     int temp = 0;
     uint32_t len = sizeof(data) / sizeof(data[0]);
 
@@ -25,6 +25,10 @@ void test_heap_num(void)
     heap->print_obj = print_num;
     heap->compare = compare_num;
 
+    // default: maxheap
+    // maxheap or minheap
+    // heap->setmin(heap, true);
+
     printf("\n\n----- test_heap_num -----\n");
 
     printf("----- push -----\n");
@@ -57,6 +61,24 @@ void test_heap_num(void)
         temp = data[i];
         heap->push(heap, &temp);
     }
+
+    printf("----- pop -----\n");
+    for (i = 0; i < len; i++)
+    {
+        temp = data[i];
+        heap->pop(heap, &temp);
+
+        printf("pop = ");
+        heap->print_obj(&temp);
+        printf("size = %2d : ", heap->size(heap));
+        heap->print(heap);
+        printf("\n");
+    }
+    if(heap->empty(heap))
+    {
+        printf("----- empty -----\n");
+    }
+    heap_free(heap);
 }
 
 void test_heap(void)