diff --git a/datastructure/queue/arrayqueue.go b/datastructure/queue/arrayqueue.go
index d15e933..4532894 100644
--- a/datastructure/queue/arrayqueue.go
+++ b/datastructure/queue/arrayqueue.go
@@ -60,7 +60,7 @@ func (q *ArrayQueue[T]) Front() T {
 
 // Back return back value of queue
 func (q *ArrayQueue[T]) Back() T {
-	return q.data[q.size-1]
+	return q.data[q.tail-1]
 }
 
 // EnQueue put element into queue
diff --git a/retry/retry.go b/retry/retry.go
index a30e6a1..c5533c1 100644
--- a/retry/retry.go
+++ b/retry/retry.go
@@ -128,9 +128,10 @@ func Retry(retryFunc RetryFunc, opts ...Option) error {
 	}
 
 	var i uint
+	var lastErr error
 	for i < config.retryTimes {
-		err := retryFunc()
-		if err == nil {
+		lastErr = retryFunc()
+		if lastErr == nil {
 			return nil
 		}
 
@@ -148,7 +149,7 @@ func Retry(retryFunc RetryFunc, opts ...Option) error {
 	lastSlash := strings.LastIndex(funcPath, "/")
 	funcName := funcPath[lastSlash+1:]
 
-	return fmt.Errorf("function %s run failed after %d times retry", funcName, i)
+	return fmt.Errorf("function %s run failed after %d times retry, last error: %w", funcName, i, lastErr)
 }
 
 // BackoffStrategy is an interface that defines a method for calculating backoff intervals.
diff --git a/retry/retry_example_test.go b/retry/retry_example_test.go
index 3c9cbeb..20cfcda 100644
--- a/retry/retry_example_test.go
+++ b/retry/retry_example_test.go
@@ -118,7 +118,7 @@ func ExampleRetryTimes() {
 	}
 
 	// Output:
-	// function retry.ExampleRetryTimes.func1 run failed after 2 times retry
+	// function retry.ExampleRetryTimes.func1 run failed after 2 times retry, last error: error occurs
 }
 
 func ExampleRetry() {
diff --git a/retry/retry_test.go b/retry/retry_test.go
index 125c2bc..ac2aac7 100644
--- a/retry/retry_test.go
+++ b/retry/retry_test.go
@@ -15,14 +15,16 @@ func TestRetryFailed(t *testing.T) {
 	assert := internal.NewAssert(t, "TestRetryFailed")
 
 	var number int
+	customError := errors.New("error occurs")
 	increaseNumber := func() error {
 		number++
-		return errors.New("error occurs")
+		return customError
 	}
 
 	err := Retry(increaseNumber, RetryWithLinearBackoff(time.Microsecond*50))
 
 	assert.IsNotNil(err)
+	assert.Equal(errors.Is(err, customError), true)
 	assert.Equal(DefaultRetryTimes, number)
 }