To design a Fast Steering Mirror (FSM) system rapidly and to predict its performance, a FSM dynamic model with two Degree of Freedom (DOF) was established, and a design method for the “dynamic model-based design of FSM” was investigated. The structure and operating principle of the FSM was described, and an ideal dynamic model of FSM was derived. Then, the high-order resonance and the coupling between the axes were analyzed and a two DOF integrated model of FSM is established. Based on the FSM model, main parameters for the FSM were determined. According to the design parameters, a FSM prototype was produced and its performance was tested. The results indicate that the simulation performance obtained by the FSM model is coincident with the experimental performance of the FSM prototype well. Moreover, the FSM shows its bandwidth more than 250 Hz, adjusting time less than 15 ms, overshoot less than 8%, and position accuracy better than 20 μrad. These results demonstrate that the FSM prototype can satisfy the design requirements. It verifies the validity and correctness of the design method.