In order to improve the measurement sensitivity of capacitive MEMS microwave power sensors, the internal space of the sensor was fully utilized, and a novel capacitive microwave power sensor based on symmetric double cantilever beams was proposed in this paper. Based on the structure of symmetric double cantilever beams, a pivoted electro-mechanical model was established, and the measurement sensitivity and overload power of the sensor were researched and analyzed. The results showed that the sensitivity of symmetric double-beam structure was three times higher than that of traditional single-beam structure with the same initial gap of the cantilever beam. Meanwhile, a wide-range tradeoff between sensor’s sensitivity and overload power could be realized by changing the initial gap of the cantilever beam. Therefore, the proposed symmetric double-beam structure could meet design demand widely.