Ring laser gyroscope (RLG) is one of the most important equipment in high-precision strap-down inertial navigation systems and has been widely used in the field of navigation. At present, there is little research on the application of RLG on the angle error measurement of sub-arc-second in the metrology field, and it has not been officially used as the metrology standard instrument. Aiming at the inaccurate measurement of RLG in metrology due to zero position drift and noncoplanar installation, a noncontact high-precision angle measurement error measurement method is proposed in this article. First, the original scale factor is calculated on the standard rotating device to avoid re-calculated on the measured device and solve the traceability problem. Second, the influence of the installation error between the turntable and the laser gyroscope goniometer on the angle measurement error is analyzed, and the compensation method for angle measurement error in the online measurement of the laser gyroscope is proposed. Finally, the feasibility of online metrology of RLG is verified by experiments, and the measurement uncertainty is estimated. The online measurement results show that compared with the photoelectric autocollimator (measurement uncertainty is $U = 0.07^{\prime \prime }({k = 2})$ , the angle measurement error of the RLG goniometer (RLGG) in multiaxis turntable is $\pm 0.4^{\prime \prime }$ , and the measurement uncertainty is $U = 0.36^{\prime \prime }({k = 2})$ .