Abstract: Relativity of simultaneity, time dilation and length contraction effect are among the main conclusions of special relativity. In the light of the fact that simultaneity is the foundation of space-time survey, we have explained our recognition on the time dilation and length contraction in more detail on the basis of relativity of simultaneity in this paper. The time dilation effect is a general reflex of the slow tempo of the mobile clock and different clock calibration in different inertial reference frame, and the essence is the direct reflection of relativity of simuh aneity for time-measurement ; while the essence of length contraction is the reflection of relativity of simultaneity for space-measurement, as well as the different spatio-temporal description of the same objective fact by observers in different inertial reference frame.

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