Objective To analyze how the athletes control postural balance through observing their joint angular motion change，center of pressure (COP) change and EMG activities of lower extremities for both athletes and beginners when performing the movement of white crane spreads its wings in Tai Chi Quan. Methods Twenty subjects were divided into 2 groups as 10 athletes and 10 beginners of Tai Chi Quan in each. When performing the movement of white crane spreads its wings, their EMG activities of 10 skeletal muscles, two-dimensional angular motion of 3 large joints in bilateral lower extremities, and COP displacements in lateral and anterior-posterior directions were recorded. Each performing trial took 8 seconds and repeated 5 times. All data were statistically processed for EMG, motion and balance analysis, and the EMG data were normalized to compare the differences between the athletes and beginners of Tai Chi Quan. Results The EMG activities of tibialis anterior(Ta), biceps femur(bF), gluteus medium(Gm) in support leg of athletes were significantly greater than those of the ipsilateral muscles in support leg of beginners, and the same was the EMG activities of gastrocnemius (G) and rectus femur（rF) in virtual leg of athletes compared with the beginners. The maximal average angular motion of 3 large joints and the coxa -joint motion of support leg in athletes were both significantly greater than that in beginners, but the anterior-posterior COP displacement in athletes was significantly smaller than that in beginners. Conclusions When performing the movement of white crane spreads its wings in Tai Chi Quan, athletes could oppose the COP change by enhancing muscle activities to maintain the postural balance, while beginners couldn’t make such active muscle activities against the uncontrolled anterior-posterior COP displacement. This may preliminarily explain the reason why Tai Chi Quan exercise can improve the muscle strength in lower extremities and enhance the ability of postural control.