Combining dynamic nonlinear finit element analysis and impact test, the process and priciple of drectional fracture of seal cover under the opposite impact of rocket fuze, and the topology self locking and bearing capacity of seal cover under the forward impact of the adjacent rocket burning gas jet flow are studied, in order to realize the fracture principle of composite seal cover. A good agreement is obtained after comparation between the finit element analysis results and the impact test results. The research results show that the topology self locking seal cover satify the requirement of directional fracture, the safety and the reliability of fuze body are ensured and the seal cover will not be destroyed under the impingement force of rocket exhaust.