Abstract: The pyrotechnically actuated mechanisms equipped on spacecraft are used for achieving key procedures and missions, and need to satisfy very high reliability and security requirements. This paper focused on the working process of pyrotechnically actuated mechanism with complex structure, the dynamics model considering nonlinear fluid-structure interaction has been established and solved by using finite volume method and finite element method under two different load working conditions. The change of variables in fluid field and output performance of pyrotechnically actuated mechanism has been obtained. The numerical simulation results showed the availability of numerical simulation on pyrotechnically actuated mechanism, and the output performance of pyrotechnically actuated mechanism was related to the loads.