In order to improve the measurement accuracy of the angle measuring system, based on the characteristics and form of the error, the corresponding mathematical models of the scoring error, photoelectric signal error, eccentricity error, tilt error and the error caused by the deformation in the angle measuring system were established from the harmonic angle aspect,and the eccentricity error and tilt error were analyzed. Furthermore,a metal circular grating angle measuring system was built, and the error in the system was analyzed and corrected. The experimental results show that the angle measurement error of the angle measuring system is 134.2″, and the corrected error is 32.23″. The error analysis of the circular grating angle measurement system provides a theoretical basis for the subsequent error compensation.