Tunable photonic crystal (PC) can control photonic band gap through changing the refractive index of liquid crystal (LC) by adding an electric filed, optical field or changing its temperature, which can change the orientation of LC′s direction vector. Plane-wave expansion method (PWM) is used to simulate the band gap of 2D tunable triangular lattice PC with structure of cylinder, square column and regular hexahedron column. The influence of changing rods shape, rotation angle and filling ratio on 2D phenylacetylene LC photonic band gap(PBG) are discussed when the substrate materials are Ge and Si respectively. It is find that there isn′t any absolute PBG in any condition, but big tuning range of TE polarized wave can be achieved by changing the index of liquid crystal. This structural parameter can provide theoretical instruction for field sensitive polarizer with great tuning range, and foundation of triturating waveguide optical switch, tunable filter and optical attenuator.