In order to achieve the accurate calibration and long-time stable operation for photoelastic modulator (PEM), a calibration and control scheme of phase retardation amplitude which using feedback optical path was established, and the spatial distribution of phase retardation amplitude on the PEM optical aperture was theoretically calculated and simulated. An integrated calibration feedback optical path was designed deviating from the center of PEM. Combined with the phase retardation amplitude calibration method using the ratio of harmonic terms, the digital phase lock technology was used to simultaneously extract the harmonic terms of the modulated light intensity signals from the feedback optical path, and then the phase retardation amplitude of PEM was solved. According to the proposed scheme, the PEM physical object was processed, and the calibration experiment and stability control experiment were both carried out. The experimental results show that, the relative deviation between the calibration value and measured value of phase retardation amplitude of PEM center does not exceed 0.22%. With the use of feedback optical path to control the PEM about 100 minutes, the standard deviation of PEM phase retardation amplitude is 0.001 8 rad and the maximum deviation is lower than 0.42%, which realizes the accurate and real-time calibration of PEM phase retardation amplitude and the long-time stable control of PEM is also verified.