In order to realize the goal of wide tunable range, fast tuning, narrow bandwidth, low actuated voltage, and mass production, a novel tunable optical filter based on micro-electro mechanical system (MEMS) is presented. The Fabry-Perot (F-P) cavity is composed of a movable optical mirror with high reflectance and the face of a fiber collimator. The output wavelength can be adjusted by changing the length of the F-P cavity through the electrostatic drive. The principles of wavelength tuning and electrostatic drive are analyzed. The structural parameters and comprehensive design method are discussed. The tunable filter is fabricated successfully by the bulk silicon technology and the experimental measurement is implemented. The test results show that the device can adjust between the 3 dB bandwidth and the free spectrum range by changing the original position of the fiber collimator. The filter takes the advantages of MEMS and fiber technology with compact structure, simple process and low actuated voltage. The device can be applied in many fields such as optical communications.