A model of two-dimensional photonic band gap structure resonant cavity composed of GaAs pillars with graphite lattice is proposed. The variation of its TEy mode formant wavelength with temperature is calculated by finite difference time domain method. The results show that there is a sectional linear characteristic between the main formant wavelength and temperature for this kind of photonic crystal resonant cavity, and the sensitivity responding to temperature is more than 1.60nm/℃. At the same time, the results show that this kind of resonant cavity possesses an excellent characterisitc of frequency switching. Finally, the cause for its switching characteristic is explained by the calculated results.