Liquid crystal variable retarders(LCVR), a kind of wave plate using liquid crystal birefringence effect, can modulate the incident light phase by changing the electric field. It needs to be calibrated accurately advancely because of its phase delay related to the voltage, wavelength, temperature and other factors. The calibration method of LCVR based on Stokes vector measurement was proposed, and the functional relationship between the system stokes vector and the LCVR phase delay was established. The Stokes vector of light was measured by polarization measurement instrument, then the phase delay of LCVR was calculated. The proposed Stokes vector method was compared with the two traditional light intensity calibration methods, and the correctness of the new method was verified. Stokes vector method is more simple and convenient, the system no longer needs analyzer, and avoided the error from the transmission axis calibration and light intensity measurement. Finally, the influences of voltage, angle of polarization of incident light, incident wavelength and temperature on the phase delay of LCVR were analysed.