concept of e- lectron spin. However，its physical images and conclusions are usually derived from

the differential process of con- tinuous Lorentz transformation. The method is complicated and

difficult to understand. In this article，based on the concept of shortening the length in the

direction of motion in the special theory of relativity，it is surprising to find that Thomas

precession angular velocity can be easily calculated by the integral effect of the

angle difference be- tween the nuclear reference system and the electron reference system

when the electron moves around the nuclear for a full circle.