A high-precision error measurement method of angular displacements based on the biaxial of the reciprocal roll angles (RRA) is presented. The resolution and precision of the angular displacement measurement systems are guaranteed using the principle of small-angle measurements, along with a photoelectric autocollimator and reflector. Based on the method of the biaxial RRA and the principle of full-circle closure, a displacement measurement system covering the full circumferential range is built. The displacement measurement system can recognize the reference angle error elimination, the calibration angle error, and mutual compensation. The total error model of the angular displacement error measurement and the biaxial turntable is established, and the main error terms are analyzed using the total error model of the turntable and the components. The traditional “Fourier harmonic analysis” and sparse decomposition methods are used to correct the system error components. The simulation accuracy of the corrected turntable is similar to that of the error-free term, and the analysis results are used in the system-optimized configuration, including precision distribution. The experiment verifies the feasibility and effectiveness of the proposed high precision, angular displacement, and error measurement method.