To effectively reduce the influence of edge field effect on the micro-electromechanical systems (MEMS) microwave power detection chip of a cantilever-beam structure and improve the microwave characteristics of the detection chip, we established a cantilever-beam capacitance model in this study. The cantilever-beam structure was optimized, and the compensation effect of the array hole size and density on edge field capacitance was studied using finite element simulation software. The finite element simulation results showed that the structure was optimal when the hole size was 10 μm×10 μm and hole spacing was 10 μm. The calculated coupling capacitance values of three MEMS cantilever beams were 67.6, 101.4, and 135.3 fF, respectively. The equivalent capacitance values obtained using the finite element simulation were 67.3, 100.5, and 134.1 fF, respectively, and the influence of the edge field capacitance of the MEMS cantilever beams decreased to 0.4%, 0.9% and 0.9%, respectively. The experimental results showed that the return loss of the detection chip was less than −10.6 dB at 8–12 GHz, and the sensitivities of the three systems at 10 GHz were 16.3, 65.6, and 144.4 fF/W, respectively, which provide reference values for studying the MEMS cantilever-beam capacitance model.