When a thin-film filter is used in oblique incidence, the central wavelengths of the polarization light will be separated obviously, and it will cause serious polarization dependent loss. Therefore, this paper designs a 100 GHz channel spacing stack to depolarize in the central wavelength based on the equivalent layer theory and to realize the angle and wavelength tunes of the thin film filter. Firstly, the depolarization equivalent refractive index in the space layer of the filter was calculated by a phase analysis and to complement the alignment of the different polarization lights. Based on the equivalent layer theory, a symmetric three layer stack was designed to replace the depolarization equivalent refractive index of the spacer. As comparing with the original five layer low polarization thin film filter, the three layer spacer stack is simpler, and it is more accurate to replace the depolarization equivalent refractive index. The simulation and experimental results indicate that the stack can align the polarization light central wavelength from 0° to 20°, in which the polarization light separation is less than 0.03 nm and the wavelength tuning range reaches 35 nm.