A method to calibrate the fast axis of a quarter-wave plate by nulling the foundamental component was proposed and the calibration principle was analyzed. The optical calibration system is composed of a laser, a polarizer, the quarter-wave plate to be calibrated, a phase modulator, an analyzer and an opto-electronic detector. The azimuths of the transmission axes of the polarizer and the analyzer with respect to the major oscillation direction of the phase modulator are +45° and 0°, respectively. A collimated laser beam passes through the polarizer, the phase modulator, the quarter-wave plate and the analyzer in turn, and then is detected by the opto-electronic detector. The theoretical analyse shows that the calibration precision depends on the azimuth error of the analyzer. The feasibility of the method was verified by experiments. The maximum deviation of the calibrated fast axis azimuth of the quarter-wave plate is 0.043°, the root-mean-square error is 0.012°, and the calibration precision is 0.05°.