A stable control technique based on Photoelastic Modulation (PEM) for resonant phase tracking of driving signal is studied. The equivalent circuit model of PEM and its resonance matching circuit is established, and the amplitude-frequency and phase-frequency relationships of driving voltage and inductance voltage of the matching circuit are deduced, as well as the relationship between PEM resonance frequency and inductance voltage resonance phase. A PEM control system is set up, with the feedback voltage phase of the initial resonance frequency as the zero phase reference. Adjusting the drive voltage stabilizes the feedback voltage phase near the phase reference value, and corrects the phase reference value with the change of the resonance frequency so that the drive voltage frequency is always stable near the PEM resonance frequency. Taking the phase delay amplitude of 1/4 wave and half wave PEM as examples, the stability control tests for 60 min are performed. The results show that: (1) When PEM works in 1/4 wave state, σδq=0.001 4 rad, the maximum relative deviation is 0.58%; (2) Standard deviation when working in half-wave state, σδh=0.001 3 rad with a maximum relative deviation of 0.32%.