A tunable photonic crystal filter is proposed with parallel nematic liquid crystal as defect layer. The transmission modes while varying incident angle are discussed in detail by 4×4 matrix method. The results show that transmission modes are mainly decided by the voltage when the incident angle is smaller than 10°. In this region, the transmission modes can be tuned by voltage and different modes can be selected based on polarization sensitive performance. When the incident angle is greater than 10°, the peaks of two modes shift toward the shorter wavelength side and the change of two modes is different. So the transmission modes can be tuned and selected by varying the incident angle in the voltage region of more than 8 V. Both the tunable range and the flexibility of application are enlarged.