A ultra-fast light-controlled modulator is designed for blocking terahertz (THz) wave propagation based on defect mode frequency shift of nonlinear photonic crystals.The modulator adopts the structure of introducing line defects and point defects filled with gallium arsenide materials in silicon-based air column photonic crystals.Due to the photonic band gap effect,waveguide region is formed at the line defect.THz waves with transmission frequencies within the photonic band gap can be transmitted in the waveguide.The point defect acts as a resonant cavity to select the frequency of THz waves,and the THz waves with the same resonant frequency (defect mode frequency) resonate in the resonant cavity and are coupled to the waveguide for output. When there is no light excitation,the 1.65 THz defect mode frequency located in the photonic band gap of the line defect resonates in the resonant cavity and output from the other end of the waveguide,and the modulator is in the “on” state.On the other hand,the defect mode frequency shifts due to the refractive index of gallium arsenide filled point defect changes from 3.55 to 3.55－i2.55 with the excitation of the central wavelength 810 nm and the optical density 0.4 μJ/cm².And the transmission of 1.65 THz incident wave is blocked with the ultra-fast time of sub seconds.The results show that the modulator with modulation rate of 2.3 GHz,extinction ratio of 20.3 dB,and insertion loss of 0.18 dB has the advantages of high modulation rate,large extinction ratio and small insertion loss,which provides an important theoretical basis for its application in high-speed THz wave communication system.