As a device for time-delay, clock mechanism is widely used in fuze safety and arming device, whose core component is the runaway escapement. With the development of artillery systems, the dynamic environment during the projectile becomes more and more complicated. Recently, some shots misfire or premature explode during shooting process because runaway escapements’ miswork. This paper utilizes gear system’s research results applied in other fields, discusses clock mechanism’s dynamics problem, and uses ADAMS to analyze runaway escapement’s rigid-flexible coupling model. From comparing the simulation results of multi-rigid model and rigid-flexible coupling model, we find that elastic deformation will affect runaway escapement’s movement, even can cause the whole device to work abnormally.