The peculiarity of nematic liquid crystal (LCBL-009) electric-control birefringence is studied. The simple and precise polarized light interference method is employed to measure the birefringence of liquid crystal. When wavelength of the incident light is 630 nm, transmissivity curve of LC is measured as the functions of the effective value and frequency of AC voltage by using Shimadzu UV-3101 PC spectrometer. After analysing the experimental result, electric-control birefringence of LC was obtained. The electriccontrol birefringence of LC is single order exponential falling with the increase of effective value of voltage and linear falling with the increase of frequency of voltage in definitive domain. The obtained result is usefull for the design and manufacturing, application of LC device.