In order to improve the firing speed of antiaircraft gun, based on the firing principle of "multi-projectile”, a 14.5 mm caliber bullet "multi-projectile" model was established. Nine tungsten core APDs api-t were integrated in one unit, and the two-dimensional two-phase flow interior ballistic model was established to obtain the firing data of interior ballistics, based on which the dynamics simulation was carried out, the strength of the cartridge was checked. The results show that the principle of "multi shot" can ensure high RF (more than 27 000 round/min) meanwhile the length of tube would not be increased.