In the paper the electric controlled optical tunable filter as a MOEMS device based on the FP resonant cavity on silicon, which will be potentially used in the dense wavelength division multiplexing (DWDM) system, is introduced. It can be used mainly as a wavelength division multiplexer in a DWDM system, and can be used as a optical add-drop multiplexer (OADM) in an all-optical switch system. Its basic operation principle is that one of the two mirrors is made into an elastic membrane structure, then the cavity length is varied under the driving of the electric field force, and the wavelength tuning be realized. The parameters of its characters, the working principle and the basic structure of the device are analyzed and calculated, including the optical properties, for instance, the tunable spectral range, the 3 dB bandwidth, the finesse, and the insertion loss, the structural properties, for instance, the deformation of the elastic membrane under the electric field force, the mechanics property and the couple performance, for instance, the electromechanical couple between the membrane of the FP cavity and the applied electric field. According to the required performances of the device and the subsystem, the preliminary design is performed combining the technique condition. From the analyzed results, the advantages of minuteness volume, low insertion loss, and high adjustment precision are clearly known.