Birefringence measurement methods such as interferometry and compensation need to rotate the sample or polarization element to be measured, which is inconvenient to operate, slow to measure and limited in accuracy.A birefringence measurement system composed of double photoelastic modulation and PC is proposed. The modulation signal is generated by the photoelastic modulation, the information of the sample to be tested is loaded, and the modulation signal is collected to the PC for data processing, so as to further complete the solution of the retardation and the fast axis azimuth angle.The principle of the test scheme is analyzed, and the upper computer design and implementation of the system data processing are emphasized, and the software and hardware system is built.The experimental results show that the relative error of delay measurement is 2%,and the relative error of fast axis azimuth measurement is 0.4%. The standard deviations of the retardation and fast axis azimuth angle are 0.056nm and 0.022°.