Tunable photonic crystals(PC)draw rapidly growing interests in recent years. Practical applications in photonic devices provide a strong motivation to further development of dynamic tenability. The current progresses on tunable photonic crystal are reviewed from the aspects of the approaches,mechanisms,and materials. The tenability of photonic band gap on the condition of the change of the crystals structure parameters is described in details by utilizing the external force,electric field,magnetic field,and so on. The researches of changing the average refractive index of materials to control the band gap are also introduced,among which liquid crystal materials and electro-optic materials are mainly described. The advantages of different tunable methods are compared. Finally,the perspectives of the future research are briefly predicted .