diff --git a/kws/bin/plot_det_curve.py b/kws/bin/plot_det_curve.py
index 0f6c76a..43410bd 100644
--- a/kws/bin/plot_det_curve.py
+++ b/kws/bin/plot_det_curve.py
@@ -72,10 +72,16 @@ if __name__ == '__main__':
         '--figure_file',
         required=True,
         help='path to save det curve')
-    parser.add_argument('--xlim', required=False, default='5', help='range of X-axis')
-    parser.add_argument('--x_step', required=False, default='1', help='step of X-axis')
-    parser.add_argument('--ylim', required=False, default='35', help='range of Y-axis')
-    parser.add_argument('--y_step', required=False, default='5', help='step of Y-axis')
+    parser.add_argument(
+        '--xlim',
+        default='5',
+        help='xlim：range of x-axis, x is false alarm per hour')
+    parser.add_argument('--x_step', default='1', help='step on x-axis')
+    parser.add_argument(
+        '--ylim',
+        default='35',
+        help='ylim：range of y-axis, y is false rejection rate')
+    parser.add_argument('--y_step', default='5', help='step on y-axis')
 
     args = parser.parse_args()