In view of the complex dynamic coupling interference of the reaction force of piezoelectric fast steering mirror to the effective optical elements, we have proposed a reaction force analysis method based on rigid-flexible coupling and based on the piezoelectric coupling theory. The reaction force of the piezoelectric fast steering mirror was analyzed and compensated, and the hotspot stress of the central flexure hinge was measured. The simulation and experimental results show that the piezoelectric coupling method can be used to evaluate the reaction force characteristics more accurately than the rigid-flexible coupling method. During the experiment, the reaction force compensation ratio can become 90.14%, which is 3.96% less than that of numerical value. The proposed reaction force analysis method and momentum compensation structure could provide a reference to calculate and eliminate the coupling disturbance of the reaction force of the piezoelectric fast steering mirror to the optical system.