Abstract: The Risley grating tracking system is mainly composed of two rotating polarization gratings. The light source is diffracted by the polarization grating to achieve beam pointing in the conical range, and then the target is captured and tracked. As an important index of the Risley grating tracking system, pointing accuracy is not only affected by servo and optical systems but also by system errors such as antenna installation accuracy and shafting assembly error of double grating turntable in the Risley grating tracking system. Therefore, this paper mainly analyzes the systematic error sources in the Risley grating tracking system and the pointing errors caused by them. First, a mathematical model of systematic error is established and verified by ZEMAX. Then, MATLAB is used to analyze the influence of each systematic error source on the pointing error of the Risley grating tracking system. Finally, according to the analysis results and index requirements, the error source of a double grating tracking system is assigned to guide the design and installation of the double grating turntable. The actual maximum pointing error of the double grating turntable δ_e=7.2" is obtained after several experimental tests, which satisfies the design index of pointing error of the double grating turntable 10".