Photoelastic modulator uses the birefringence effect produced by the forced vibration of isotropic crystal to modulate the phase of incident polarized light, which has important applications in polarization modulation and measurement. The phase delay of photoelastic modulator is its key index parameter, and the driving voltage and phase delay should be calibrated in practical application. However, the components in the traditional calibration system of photoelastic modulator are bulky, and the calibration is completed before use, resulting in large errors. In order to make real-time calibration of the photoelastic modulation system available, achieve the purpose of precise calibration, and improve the convenience of use, a micro-system for precise calibration of photoelastic modulator is proposed. By reducing the size of the calibration system components, and making them integrated at the edge of the transparent aperture of the photoelastic modulator to realize real-time calibration of phase delay. It is verified by experiments that the calibration microsystem of photoelastic modulator can accurately calibrate the phase delay of photoelastic modulator in real time without affecting the central light path. The calibration results show that the phase delay deviation is less than 1% after one hour's testing.