In this paper,we propose a terahertz (THz) wave switch device based on two -dimensional photonic crystal with square lattice air holes by using the self- collimation effect of photonic crystals and the optical properties of gall ium arsenide (GaAs) dielectric plate.The laser with wavelength of 810nm is used as the pump light source for c hanging the refractive index of GaAs dielectric material in order to make the terahertz wave turned on and off.The light beam can be transmitted with out diffraction effects through the photonic crystals due to self-collimation effect.The wave switch is studied by using Rsoft software combined with plane wa ve expansion (PWE) method and two-dimensional time-domain finite difference (2D-FDTD) method.The PWE method is used to optimize the bandgap of the photonic crystal structure.Then the 2D-FDTD method is used to analyze the transmission characteristices of the photonic crys tal THz wave switch. Results show that the response time of the wave device is 107.12ps,the extincti on ratio is 27.65dB,the insertion loss is 0.086dB,and the incident THz wav e has a certain angular tolerance. What′s more,the proposed Thz wave switch device is simple and easy to be integr ated,which have important application value in future THz wireless communication technology.