Beginning with the analysis of phase relationship and by use of the characteristic matrix expression of multilayer films, three implicit function expressions of the refractive index and thickness of spacer and central wavelength or half pass-band of two polarization components are deduced. Therefore the values of middle layers refractive index and thickness and corresponding wavelength difference can be quickly and accurately obtained. Simulation calculations of concrete filter designs for four cavities prove that the method is feasible. It is obtained that short or long pass-band depolarization cutoff filter and central wavelength depolarization filter by adjusting effective refractive index and thickness of spacer. The optimized algorithm is effective for polarization controlling of thin film filter at oblique incidence.