The small variation of the structural parameters of MEMS sensor will influence the performancestability. In order to improve the robustness of MEMS sensor, taking the piezoelectric bimorph MEMS sensor as an example, the randomness of the design variables and noise factors of the piezoelectric bimorph beam are analyzed according to the Smits model.A robust design mathematical model of MEMS sensor based on the stochastic model is established. The algorithm program is compiled. The optimal design solution of MEMS sensor is better than the original design. Compared with the robust design tolerance model, the error rate is 6.17%, which verifies the correctness of the robust design. The results show that the robust design can not only improve the performance of MEMS sensor, but also guarantee the robustness of the designeven if the design variable has small variation.