diff --git a/make.sh b/make.sh
index 856b6da..f257882 100755
--- a/make.sh
+++ b/make.sh
@@ -50,7 +50,7 @@ else
  OFF_BITS=32
 fi
 
-DEBUG_FLAG=1
+DEBUG_FLAG=0
 
 CFLAGS='-Wall -D_FILE_OFFSET_BITS=64'
 if [ "$DEBUG_FLAG" = "1" ]; then
diff --git a/src/skiplist.c b/src/skiplist.c
index 08a32ba..debc650 100644
--- a/src/skiplist.c
+++ b/src/skiplist.c
@@ -52,7 +52,7 @@ int skiplist_init_ex(Skiplist *sl, const int level_count,
 
     for (i=0; i<level_count; i++) {
         element_size = sizeof(SkiplistNode) + sizeof(SkiplistNode *) * (i + 1);
-        if ((result=fast_mblock_init_ex(sl->mblocks + i, 
+        if ((result=fast_mblock_init_ex(sl->mblocks + i,
             element_size, alloc_elements_once, NULL, false)) != 0)
         {
             return result;
@@ -90,11 +90,11 @@ void skiplist_destroy(Skiplist *sl)
     sl->mblocks = NULL;
 }
 
-static inline int skiplist_get_previous_level_index(Skiplist *sl)
+static inline int skiplist_get_level_index(Skiplist *sl)
 {
     int i;
 
-    for (i=0; i<sl->level_count; i++) {
+    for (i=0; i<sl->top_level_index; i++) {
         if (rand() < RAND_MAX / 2) {
             break;
         }
@@ -111,7 +111,7 @@ int skiplist_insert(Skiplist *sl, void *data)
     SkiplistNode *previous;
     SkiplistNode *current;
 
-    level_index = skiplist_get_previous_level_index(sl);
+    level_index = skiplist_get_level_index(sl);
     node = (SkiplistNode *)fast_mblock_alloc_object(sl->mblocks + level_index);
     if (node == NULL) {
         return ENOMEM;
@@ -211,4 +211,3 @@ void *skiplist_find(Skiplist *sl, void *data)
     return (previous != NULL) ? previous->links[level_index]->data : NULL;
 }
 
-
diff --git a/src/tests/Makefile b/src/tests/Makefile
index 14fb3fe..73c875c 100644
--- a/src/tests/Makefile
+++ b/src/tests/Makefile
@@ -1,6 +1,6 @@
 .SUFFIXES: .c .o
 
-COMPILE = $(CC) -Wall -D_FILE_OFFSET_BITS=64 -g -DDEBUG_FLAG
+COMPILE = $(CC) -O2 -Wall -D_FILE_OFFSET_BITS=64 -g -DDEBUG_FLAG
 INC_PATH = -I/usr/include/fastcommon
 LIB_PATH = -lfastcommon
 
diff --git a/src/tests/test_skiplist.c b/src/tests/test_skiplist.c
index b948165..2f6b7db 100644
--- a/src/tests/test_skiplist.c
+++ b/src/tests/test_skiplist.c
@@ -7,55 +7,47 @@
 #include <inttypes.h>
 #include <sys/time.h>
 #include "skiplist.h"
+#include "logger.h"
+#include "shared_func.h"
+
+#define COUNT 1000000
+#define LAST_INDEX (COUNT - 1)
+
+static int *numbers;
+static Skiplist sl;
+static SkiplistIterator iterator;
 
 static int compare_func(const void *p1, const void *p2)
 {
     return *((int *)p1) - *((int *)p2);
 }
 
-int main(int argc, char *argv[])
+static int test_insert()
 {
-#define COUNT 1280
-#define LAST_INDEX (COUNT - 1)
-
-    Skiplist sl;
-    SkiplistIterator iterator;
-    int *numbers;
     int i;
-    int tmp;
-    int index;
     int result;
     void *value;
+    int64_t start_time;
+    int64_t end_time;
 
-    numbers = (int *)malloc(sizeof(int) * COUNT);
-    srand(time(NULL));
-    for (i=0; i<COUNT; i++) {
-        numbers[i] = i + 1;
-    }
-
-    for (i=0; i<COUNT; i++) {
-        index = LAST_INDEX * (int64_t)rand() / (int64_t)RAND_MAX;
-        tmp = numbers[index];
-        numbers[index] = numbers[LAST_INDEX - index];
-        numbers[LAST_INDEX - index] = tmp;
-    }
-
-    result = skiplist_init_ex(&sl, 12, compare_func, 128);
-    if (result != 0) {
-        return result;
-    }
-
+    start_time = get_current_time_ms();
     for (i=0; i<COUNT; i++) {
         if ((result=skiplist_insert(&sl, numbers + i)) != 0) {
             return result;
         }
     }
+    end_time = get_current_time_ms();
+    printf("insert time used: %"PRId64" ms\n", end_time - start_time);
 
+    start_time = get_current_time_ms();
     for (i=1; i<=COUNT; i++) {
         value = skiplist_find(&sl, &i);
         assert(value != NULL && *((int *)value) == i);
     }
+    end_time = get_current_time_ms();
+    printf("find time used: %"PRId64" ms\n", end_time - start_time);
 
+    start_time = get_current_time_ms();
     i = 0;
     skiplist_iterator(&sl, &iterator);
     while ((value=skiplist_next(&iterator)) != NULL) {
@@ -63,6 +55,72 @@ int main(int argc, char *argv[])
         assert(i == *((int *)value));
     }
     assert(i==COUNT);
+
+    end_time = get_current_time_ms();
+    printf("iterator time used: %"PRId64" ms\n", end_time - start_time);
+    return 0;
+}
+
+int main(int argc, char *argv[])
+{
+    int i;
+    int tmp;
+    int index1;
+    int index2;
+    int result;
+    int64_t start_time;
+    int64_t end_time;
+    void *value;
+
+    log_init();
+    numbers = (int *)malloc(sizeof(int) * COUNT);
+    srand(time(NULL));
+    for (i=0; i<COUNT; i++) {
+        numbers[i] = i + 1;
+    }
+
+    for (i=0; i<COUNT; i++) {
+        index1 = LAST_INDEX * (int64_t)rand() / (int64_t)RAND_MAX;
+        index2 = LAST_INDEX * (int64_t)rand() / (int64_t)RAND_MAX;
+        if (index1 == index2) {
+            continue;
+        }
+        tmp = numbers[index1];
+        numbers[index1] = numbers[index2];
+        numbers[index2] = tmp;
+    }
+
+    result = skiplist_init_ex(&sl, 12, compare_func, 128);
+    if (result != 0) {
+        return result;
+    }
+
+    test_insert();
+
+    start_time = get_current_time_ms();
+    for (i=1; i<=COUNT; i++) {
+        assert(skiplist_delete(&sl, &i) == 0);
+    }
+    end_time = get_current_time_ms();
+    printf("delete time used: %"PRId64" ms\n", end_time - start_time);
+
+    start_time = get_current_time_ms();
+    for (i=1; i<=COUNT; i++) {
+        value = skiplist_find(&sl, &i);
+        assert(value == NULL);
+    }
+    end_time = get_current_time_ms();
+    printf("find after delete time used: %"PRId64" ms\n", end_time - start_time);
+
+    i = 0;
+    skiplist_iterator(&sl, &iterator);
+    while ((value=skiplist_next(&iterator)) != NULL) {
+        i++;
+    }
+    assert(i==0);
+
+    test_insert();
+
     skiplist_destroy(&sl);
 
     printf("pass OK\n");