Abstract: Terahertz modulator is one of the key devices in Terahertz communication system.Based on the crystal materials and Terahertz wave theory, an examination is made of the modulation characteristics of crystal materials in modulating the terahertz wave, and a numerical simulation is conducted to find out about the modulating effects of the frequency, amplitude and phase upon the terahertz wave.Some physical conditions for these crystal materials to give the best modulating performance are presented.The results thus obtained can be of some directive function in the design of high efficiency terahertz modulator.