Liquid crystal materials are an important component of display devices, and their high birefringence under the action of external fields is a crucial condition for their use in display. Using a strong terahertz wave as an external field to excite the birefringence effect of liquid crystal 5CB material, the birefringence effect of terahertz field induced liquid crystal in the terahertz band was studied. With a terahertz time domain spectroscopy system, we measured the transmittance of terahertz waves with different polarization states. The relationship between the birefringence effect of liquid crystals and the external field strength, as well as the frequency response characteristics, were analyzed. The results show that the birefringence of liquid crystal increases with the increase of field strength provided by strong terahertz waves, and the birefringence value is proportional to the square of field strength, and there is a threshold value for the birefringence effect of liquid crystal 5CB excited by terahertz waves.