Fast steering mirrors(FSM) are high-precision, high-bandwidth electro-mechanical mechanisms for enhancing the performance of electro-optical imaging and beam-steering systems, which have found wide applications in such areas as astronomy, laser communications, military targeting and surveillance systems.In this paper, typical FSM electromechanical configurations and features are overviewed.Then, the development of the LOS kinematic relation of FSM is presented, and some representative patterns of scanning deviation are given.The obtained kinematic relations can be used to calibrate the FSM system in order to improve the pointing performance.