The purpose of this study was to investigate the kinematic factors influencing Leg Beat Action during Giant Swing Backward in Horizontal Bar and to compare the differneces between international (Subject 1, S1) and national level (Subject 2, S2) gymnasts. 3D kinematic data were collected during final, competition of horizontal bar in 1997 International China Motor Cup Gymnastics Meeting by using Peak Performance 3D Motion Analysis System (60Hz). The Giant Swing Backward in horizontal bar was divided into 6 positions and 5 phases. The 12-segments human body model war adopted and 17 landmarks wer digitized to conduct kinematic analysis. The results were following: 1. The kinematic influenceing factors of leg beat action during giant swing backward in horizontal bar according to present results were angles of shoulders and hips at position 3, position 4 and position 5. 2. The movements performed by international level gymnast (S1) and national level gymnast (S2) during first phase (from handstand position to hang-up position at vertical line in first circle) wer similar. 3. S1 showed significant shorter rotation radius of c.g. around the bar and lower values of shoulder and hip angles at third position (handstand on vertical positon in second circle) than S2 indicate that S1 well prepared to accelerate the beat action by flexion shoulder and hip. 4. S1 stretches his shoulder and hip quickly at fourth position, and after through fifth position, he flexed the shoulder and hip joints to shorten the radius of rotation in order to accelerate the rotation velocity during leg beat action. S2 did not use the changes of joint angle to conduct the technique of leg beat action. 5. The important differnces between S1 and S2 was that S1 performed the leg beat action of over grip giant swing through dynamic changes of body posture throughout 3, 4, 5 position. Instead of leg beat action, the rotation movement of S2 was stable and no significant tempo were showed, it looks like a normal giant swing.