Constant variably acceleration motion model of flying plate is proposed and the model formula about the relationship between speed of flying plate and clearance is put forward, which provides theorotical basis for choosing optimum clearance by collision speed of different metallic materials in explosive welding industry production. High pressure impulse X radial photograph experiment was carried out, the photos of the flying stances of flying plate in different clearances were obtained and the corresponding flying speeds of flying plate were calculated. Curve fitting of the experiment data through constant variably acceleration motion model was carried out. The results show that constant variably acceleration motion model accords well with the experiment data，and the maximum speed of flying plate calculated through constant acceleration model is in good agreement with the values through theoretical calculation. Therefore, it is concluded that the motion of flying plate in the main follows the constant variably acceleration motion.