A photonic crystal narrow pass band optical filter was presented, which is made of two pieces of uniaxial anisotropic photonic crystals with different photonic band gaps. The principle for the system is to arrange properly the band gaps of the two photonic crystals so that a small narrow pass band appears in the combined photonic band gap region. The optical characteristics such as transmission and polarization of this periodic structure in different incident tangos and refractivity conditions were analysed. The results show that if the uniaxial anisotropic photonic crystal has a large ratio of refractivities or combined with high refractivity isotropic media, it may have a narrow pass band gap, and our numberical investigations show that this kind of structure is feasible for narrow band optical filtering.