Abstract: The purpose of this paper is to study the dynamic response characteristics and regularity of the man-rifle system in the whole shooting process. The three-dimensional motion capture system, surface electromyography test system and plantar pressure test system were used to obtain some data, including the motion of the rifle, the response of the upper limb muscles and joint angles, man-rifle system pressure center and three-round burst dispersion. The results show that, the decrease of the right elbow angle can lead to the fatigue of the medial deltoid muscle, resulting in the decrease of first shot accuracy in the aiming stage. Also the decrease of the angle between the right arm and the trunk can get it hard for the biceps muscle of right arm to exert, making the triceps brachii muscle compensate weak for the instability during the shooting process. These are the reasons that the shooting dispersion becomes worse when the buttstock is too short. The analysis results indicate that the iEMG value of right arm's triceps brachii muscle is the best characteristic to reflect the shooting dispersion when the buttstock length changes.