The vibration of machine gun muzzle has a great influence on the firing accuracy. In this paper， a method to measure the three-dimensional motion of a gun muzzle with a high-speed photographer is presented. The vibration response of a typical machine gun during its continuous firing is measured and analyzed. The displacement， velocity and deceleration curves of the muzzle vibration response are extracted. Furthermore， the shooting dispersion is calculated based on the muzzle vibration response and compared with the experimental shooting dispersion， which verifies the accuracy of the test method. It is concluded that the three-dimensional motion parameters of the muzzle vibration response of a machine gun in continuous firing can be effectively measured by the single-camera two-direction method. Moreover， the periodicity and amplitude range of the vibration response of the machine gun muzzle are confirmed. The experimental results show that the dispersion calculated based on the muzzle vibration response is basically consistent with the experimental dispersion， which shows good engineering application value.