Abstract: As the interrupter part of the safety system may be aligned when the projectile is still in bore due to the failure of clock mechanism, which may cause the in-bore explosion, a new design criterion of safety system structure was proposed to overcome this danger. The dynamic equation of the rational part was built and solved to get the characteristics of motion when in the trajectory environment. Meanwhile, the ADAMS simulation was used to analyze and verify the rational part motion. The research proves that the new structure can eliminate the potential danger of explosion in bore, and the analysis can help the design of safety system.