Optical communication system requires the high isolation and low polarization sensitivity of Tunable Optical Filter (TOF). At present, the most of TOF based on thin film are hard to meet this requirement. The reason of TOF transmission spectrum degradation is analyzed by simulation. Referring to the center wavelength and bandwidth separation when different polarization beam in tilted incidence, an optimization design is proposed based on symmetric optical path. It improves the isolation of TOF to more than 30 dB, and restrains the polarization dependent loss within 0.2 dB. Meanwhile, different polarization beam have the same optical path because of the symmetric optical path, which can avoid adding additional wave plate. The module performance is tested, which realizes that 96 ITU-T channels can be tuned in the range of C band. The experiment results are in good agreement with the analytical ones.