The photonic energy bands of the two-dimensional photonic crystal made by GaAs pillars in air with graphite lattice is calculated by finite difference time domain (FDTD) method. The result shows that there is a complete photonic band gap in the normalized frequency zone between 0.53 to 0.58 within this kind of photonic crystal. Based on it, a model of two-dimensional photonic crystals stress sensor made by GaAs pillars in air with graphite lattice is designed. The TEy mode formant wavelength of the sensor resonant cavity changing along with x and y directions stress and the stress environment are calculated by FDTD method. The result shows that there is a good linear characteristic between the formant wavelength and the stress, the sensor sensitivity responding to stress is 0.0111 nm/MPa, meanwhile, it is found that the sensor sensitivities along x and y directions are the same.