Abstract: The termo-optic effect of nematic liquid crystal(LC)(BL-009)is probed by studying the birefringence of LC as the temperature varies.The simple and precise polarized interference method is employed to measure the birefringence of the LC.The transmissivity of the LC is measured as temperature varies from 20℃ to 100℃,the wavelength of the incident light is 630nm,so electric control birefringence of the LC is obtained as temperature varies.After analysing the experimental data,it is found that the law of the falling of electric control birefringence is different when the applied voltage is different.The obtained result is favor of the design and manufacture,application of LC device.