In order to overcome the measurement errors of traditional microwave power sensors due to mismatch and thermal losses, a symmetrical microwave power sensor based on the Micro-electro-mechanical System(MEMS) was proposed and its microwave loss, temperature distribution and the accurate measurement were researched. Firstly, expressions of the loss power and loss voltage were derived according to the proposed loss model, and the heat transfer analytical model of the power sensor was established. Then, the sensor was designed and fabricated. Finally, the compensation factor, sensitivity and the frequency-dependent characteristics of the power sensor were measured and analyzed. The measurement results show that the compensation factor of the power sensor at 5, 10 and 15 GHz are 1.56, 2.12 and 2.56 dBm, respectively. The sensitivity is about 0.18 mV/mW, and the relative difference of the output voltage with the microwave frequency is below 2%. It is concluded that the symmetrical microwave power sensor can measure the microwave power by measuring the DC power, and also can improve the measurement accuracy of the microwave power significantly.