The photoelectric system with embedded mirror in optical path is one of the main means to achieve high precision stabilization. Due to the complex compensation principle of optical path embedded composite axis stability in the reflector photoelectric system and many error factors in each link of the system, there is a large gap between stability accuracy of the line of sight (LOS) and the actual theoretical value in the actual project development. In order to meet the high precision and stability demands of various weapon platforms for the optical path embedded composite axis of the reflector photoelectric system, and to solve the problem of difficulty in controlling the coupling of various error sources in practical development, this paper analyzes the influence of each error factor on the stability error of the system, in order to provide a theoretical basis for improving the stability accuracy of the composite axis with embedded mirror in the optical path.Firstly, the system composition of the reflector type optical path embedded composite axis stabilization platform is introduced, and the coordinate systems related to the optical path embedded composite axis platform are established (Fig.2). Then, the stability principle of the system is analyzed, and the quantitative relationship between the angle of the mirror and the compensation angle error of the LOS is developed. Next, based on the above principles, the effects of the linearization of the relationship between the angle of the fast steering mirror(FSM) and the compensation angle error of the LOS, the orthogonality error between shafting and the angle measurement accuracy of the FSM, on the compensation angle error of the LOS are analyzed theoretically, and quantitative relationships between above influencing factors and the compensation angle error of the LOS are developed. Finally, based on these quantitative relationships, simulation verifications are carried out (Fig.3-18).The compensation angle error of the LOS caused by the linearization of the relationship between the angle of the mirror and the compensation angle error of the LOS increases with the angle of the mirror, and is independent of the pitch angle of the first-stage platform (Fig.3-6). Both azimuth and pitch compensation angle error of the LOS increase with the increase of the FSM installation error, and the pitch angle of the first stage platform has no effect on the compensation angle error of the LOS; both azimuth and pitch compensation angle error of the LOS increase with the increase of the gyro installation angle error as well as with the increase of the pitch angle of the first stage platform. The simulation results show that when the system maximum error is limited to no more than 2 μrad, the relationship between the angle of the FSM and the deflection angle of the LOS cannot be realized by the simplified linearization relationship. Meanwhile, the orthogonal installation errors of both the gyroscope and the FSM, both azimuth and pitch angle measurement errors of the FSM need to be narrowed to micro-radian level.Based on the stability principle of the reflector type optical path embedded composite axis platform, this paper theoretically analyzes the linearization between the angle of the FSM and the angle of the LOS, the orthogonality error of the gyroscope and the installation of the FSM, and the influence of the angle measurement accuracy of the FSM on the stability error of the system’s LOS compensation, and carries out simulation analysis. It provides a design basis for the engineering development of high precision optical path embedded composite axis platform for reflector type photoelectric system.