The photoelastic modulator can be affected by its heat dissipation, which induces the change of elasto optical crystal its temperature, natural frequency drift with the temperature caused photoelastic modulation instability and modulation efficiency is decreased. The frequency self tracking technology is presented. According to the effect of temperature on photoelastic modulation system, dynamic model of photoelastic modulation system is established to get the relation between the feedback signal and the high voltage drive signal that the minimum phase difference corresponding resonant frequency. Combined with multichannel Direct Digital Synthesis and Digital Phase Locked Loop technology based on FPGA design, the self frequency tracking system is completed. By experimental verification, the design can achieve the following on the frequency drift, and be able to automatically find elastic optical crystal resonance frequency and remain stable when the drive signal change or start the photoelastic modulator, which improves the stability and modulation efficiency of elastic light modulator.