Aiming at the big deformation of the metal open link belt during the bullet discarding process, the method of rigid-flexible coupling is used to establish the dynamic model of an ammunition feeding mechanism during the course of without-load, with-load feeding and discarding bullet out of link belt. The speed change regularity of the pressure-tooth for the ammunition at different rates of fire was obtained, and the finite element transient analysis for the bullet discarding process of link belt was carried out to get the deformation and stress value change regularity of the link belt. Then compared with the test results, it is concluded that the large stress exists during the bullet discarding process and can withstand the elastic deformation. The research results provide important reference for the structure optimization design of the metal open link belt in future.