Abstract: In order to better realize the pointing function of GSSMP, the rotation accuracy of GSSMP needs to be measured and calibrated, the rotation encoder was calibrated with the laser tracker, and the angle measurement was completed with the laser tracker. First of all, based on the principle of angle measurement, the contact measurement and non-contact measurement methods of single point calibration precision and error of measurement were 23.7 and 0.71. It was proved by formula derivation that four Sphere Mounted retro-Reflectors (SMRs) can eliminate the harmonics of all orders other than the multiple harmonics of 6 improving the measurement accuracy. Finally, the angular measurement error of two different arrangement methods of four SMRs was compared, and the uniform distribution error was 11.5, the non-uniform distribution error was 9.04, and the measurement error of a single angular reflector was 23.7. By measuring the rotation precision of the telescope's azimuth axis with laser tracker, the correctness of the theory and the feasibility of the method were verified. The research were of great significance to the further completion of the work of the 30 m telescope.