Using photonic crystal fiber (PBG) to replace the ordinary fiberwinding ring is the development direction of fiber optic gyroscope. Due to different types of optical fibers, the characteristics of thermal phase noise are different from those of conventional gyroscopes. In this paper, the thermal phase noise of photonic crystal fiber optic gyroscope was studied, and the fiber model and noise model were established by using finite element method. The thermal phase noise was measured by the light source intensity noise suppression circuit. The correctness of the model is verified by the comparison between the experimental and the simulation results.