Video images analysis and computer vision theory have been widely used in the reconstruction and projection of human motion, tracking athletes ’motion and trajectory from sports video, getting human motion model and calculating motion parameters, make it easy for physical educators to research athletes’ motion flaws, improve training level for the athlete’s in a scientific way, and achieve upgrading more quickly and effectively. In this paper, discus throw was taken as a research object, arm motion trajectory and detailed force status during its rotating process were studied and got the results that maximum throwing distance would be obtained in the way of reducing proactive force of arms and trying to achieve the maximum discus horizontal velocity. In the paper, video projection and computer vision theory were applied to reconstruction simulation on the main joint of arms, then connect into a line, finally form the 2D image till fully achieve arms motion model reconstruction .