Abstract: To study the relationship between structural parameters of ring laser gyro (RLG) path length control mirrors and its performance, a method was presented in which finite element (FE) model including elastic and piezoelectric body was established and direct coupled field analysis was conducted. By programming an ANSYS macro file, automatic synchronization between FE model and the structure size was achieved. Simulation results of a specific path length control mirrors indicate that the annular groove inner and outer diameters, and the deformable rib thickness of the mirror have the greatest impact on the light path length adjustment capability. The results are used to optimize the design. Experiments demonstrate that the method is of significance in the path length control mirror design.