Tunable filter based on Fabry-Perot cavity is a vital device in WDM system, acting as wavelength selection and monitoring, and thermally tuning based on thermo-optical effect is often used. A-Si:H and SiNx films were selected to compose the structure of the filter. The properties of these films under various process parameters are studied, and RF power of 13W and pressure of 80Pa for fabricating a-Si:H and flow rate ratio for SiH4/NH3 of 1∶2 for fabricating SiNx are suitable parameters to obtain films with high quality and favorable optical properties, besides, a-Si:H under these parameters also achieve high thermo-optic coefficient. The filter achieves good filtering performance by using these parameters to fabricate films, and transmittance peak of 75% is obtained in optical communication band, exhibiting the potential application in WDM in optical communication.