In order to improve the performance of capacitive MEMS microwave power chip, a novel high performance MEMS microwave power chip was designed. By establishing a dual-guided clamped beam capacitance model, the transmission characteristics, overload power and sensitivity characteristics of the sensor were analyzed. Two equivalent conditions were proposed for the parallel plates in the dual-guided clamped beam capacitance model. At the same time, a new beam width equivalent method was proposed to solve the mismatch problem of the equivalent beam width of the dual-guided structure, reducing the relative error of the model. The dual-guided clamped beam capacitance model explained the impact of the thickness to length ratio and initial height of the guide beam on the overload power and sensitivity of the sensor. The test results show that the sensitivity of the dual-guided clamped beam MEMS microwave power sensor is 14.3 fF/W within 200 mW input power, while the theoretical value of sensitivity is 13.5 fF/W with a relative error of only 5.6%. Therefore, this theoretical model has certain reference significance for the design of clamped beam MEMS microwave power sensors.