In order to study the nonlinear motion of the cantilever beam of capacitive MEMS microwave power sensor, the bending characteristic model of the MEMS cantilever beam in space domain was established. Considering the effects of electrostatic force, axial stress and residual stress on the nonlinear motion of the cantilever beam, a dynamic differential equation was obtained. On this basis, the bending characteristics of the cantilever beam under different Young's modulus, driving voltage and residual stress were studied. And the corresponding bending characteristic curve and axial stress curve of cantilever beam were obtained. Meanwhile, the finite element analysis software ANSYS was used to simulate the pull-down displacement of cantilever beam with different driving voltages, and the simulation results were compared with the analytical results. The results show that when the driving voltage changes from 10 V to 20 V, the simulation results are consistent with the model analysis results, and the maximum error is only 8.81%. Therefore, this work has a certain reference value and guiding significance for the research of cantilever bending characteristics of capacitive MEMS microwave power sensor.