Abstract: The conclusion of time dilation effect is obtained usually through an example in special case in the textbook.In order to deeply explore whether the time dilation effect is still corrected under general conditions，this paper expounds the universality of time dilation effect by changing the position of the mirror and the optical path.We hope it can provide a reference for teachers and students studying special relativity，and understand deeply of the time dilation effect.

Key words: special relativity, time dilation effect, length contraction effect