Path length control mirrors (PLCM) are important devices used to keep the cavity length of ring resonators stable. The deformation caused by the temperature variation directly affects the optical path shape and beam quality of ring resonators. In this paper, a finite element simulation model of PLCMs was established using ANSYS. Subsequently, the model was used to analyze the temperature and coupled fields of a PLCM under different temperature conditions. The deformation distribution in the middle of the mirror was obtained. Next, the accuracy of the finite element model was verified by sweep and temperature experiments, with an error of less than 2.5%. Finally, the deformation in the middle of the mirror under the variable temperature conditions was studied, obtaining the relationship between the deformation and the temperature. The influence of the thermal conductivity, Young 's modulus, and linear expansion coefficient of each component of the PLCM were simulated and analyzed. For different material parameters, the thermal conductivity and density have little effect on the deformation, while the Young's modulus and linear expansion coefficient greatly influence the deformation. The deformation was found to be inversely proportional to the Young's modulus and proportional to the linear expansion coefficient. In this paper, the temperature and the coupled fields of the PLCM under normal, high-low, and variable temperature were studied for the first time. In addition, the influence of the material parameters was quantitatively analyzed. The results of this paper have a guiding significance for material selection and optimization of PLCMs.