A novel InP-based micromechanied tunable photodetector with the structure of OMITMC (One-Mirror-Inclined Three-Mirror-Cavity)is presented. The tuning characteristic of the device is analysed in the way of electrical actuation. Through simulation of the filter transmission spectra and the quantum efficiency, the characteristics of high tunability, narrow bandwidth and high quantum efficiency are analysed. As a result, the photodetector is tuned with 30nm,with a quantum efficiency of 59% and a linewidth of 1.2nm, when actuated by 10 volts.