Abstract: The prism for coupling beam in ring laser gyro has a strict requirement on angle accuracy and its consistency. In order to process optical elements with high-precision angles, a new process is introduced, in which the optical element was processed by the matrix angles copied from the angles of manual repairing matrix. The impact of the goniometer accuracy, the matching error of the surface profiles and parallelism measurement error on angular machining error was analyzed. It is concluded that this process can improve the process efficiency and the machining accuracy by improving the flatness of the optical surface, avoiding local irregularity, controlling the impact of temperature difference effect and reducing the errors of parallelism measurement.