In order to solve the existing problems in bullet assembling, an automatic control system based on PLC for bullet assembling was proposed. The existing problems and present situation of bullet assembling were analyzed in this paper, and the composition of bullet assembling machine and the function of control system were described, the hardware part of control system was designed, the software part was designed in detail from 4 aspects including unit program, alarm system, initialization, and automatic production interface. As the test result showed, the control system was able to realize the bullet automatic assembling, which greatly improved the efficiency and the degree of automation.