Though the systematic analysis of the motion pictures of the javelin throwing process shot with a high speed camera, the present study finds that acceleration of the left leg forward swing after the two leg crossing results in a firm two leg support of the body, makes significant contributions to the maintenance and increase of the horizontal speed of the heart of gravity and shortens the final strength exertion time. Left side support techniques are proved to be a guarantee of the final stage momentum transmission and of the effective implement of the "whipping" skill, and to affect the initial height of the javelin.