Abstract: The fast steering mirror (FSM), as a device capable of precisely and rapidly controlling the beam direction between the target and the receiver, has a flexible support system that provides motion support and degree-of-freedom constraints for the FSM, directly determining the overall performance of the FSM system. This paper compares several traditional two-degree-of-freedom flexible support systems with an inner and outer concentric nested structure. Based on their characteristics and basic structural forms, and in combination with the design calculation results, the initial parameters are determined, a finite element model is established, and dynamic characteristic simulation is conducted using the simulation method. The design is verified through experiments.