According to the characteristics of the thin film narrowband filter, the angle-tuned filter with stable transmission peak and bandwidth can be designed by amelioration of the structure of the stack and adjust of effective refractive index of the spacer. At the same time, the central wavelength of S-polarization and P-polarization will separate when the filter is tilted, which causes the polarization dependent loss. The phenomena of polarization separation and its relationship to the effective refractive index of the filter are analyzed. A method about eliminating the polarization separation is presented. Theoretical analysis model is built up and an angle-tuned filter design method is provided based on the theory of thin film matrix. A 100 GHz dense wavelength division multiplexing (DWDM) four-cavity angle-tuned narrowband filter with low polarization dependent loss is optimized and fabricated based on the programme. The experimental results prove it meets the demand of design and its tunable range is about 20 nm.