The microwave characteristics of coupled MEMS microwave power sensor could be analyzed and calculated by the lumped parameter model, which had become an important reference for the design of sensor’s structure and size. For the increasingly complex impedance matching structure of sensors, the lumped parameter model of the sensor was optimized and derived in this work. The measurement results showed that the maximum calculated error of reflection coefficient was 6.0 dB, and the insertion loss was 0.7 dB. The accuracy of the model was obviously improved after the optimization. Therefore, the lumped parameter model optimized in this work had certain application value and reference significance for the design and optimization of coupled MEMS microwave power sensors.