In order to improve the firing reliability of the automatic gun, the influence of delayed ignition on the dynamic characteristics of internal energy automatic gun was analyzed. By analyzing the structural principle of the automatic gun when it is automatically locked, the virtual prototype model of the automatic gun when it is locked and firing is established. The dynamic simulation of the free rebound of the latch seat during the first launch, initial floating and stable floating is carried out, and the experimental results are compared to verify the credibility of the established virtual prototype. On this basis, the criterion of the displacement of the latch seat relative to the gun box is constructed, and the influence of delayed ignition on automatic gun during the first launch, initial floating and stable floating are simulated. The results show that the time range of causing automatic gun failure is 10~30 ms for the first launch, 6~34 ms for the initial floating, and 9~32 ms for the stable floating. This analysis can provide reference for the subsequent design of internal energy automatic gun with the same structure.