This paper proposes a sophisticated type of capacitive clamped beam RF MEMS power sensor, which is fabricated on GaAs substrate with MMIC technology. This new capacitive clamped beam RF MEMS power sensor can act quickly to the RF signals and consumes little power on central CPW line. A version of draft microwave circuit model is presented, in order to build a set of initial structure parameters of the clamped beam RF MEMS power sensor simulation model. The frequency scope of this designed clamped beam RF MEMS power sensor is from 8GHz to 12GHz. Through adjusting the set of initial structure parameters of simulation model, a set of successful and proper S parameter of HFSS simulation can be obtained, and the S parameter is: S11 is less than -35dB and S21 is less than 0.15dB. Based on the performance parameter mentioned, the optimization on the power sensor simulation structure has been presented.