Abstract: The measurement model of wave-plate's phase retardation based on the theory of compensate was introduced with the help of common Jones formula of wave-plate,a novel method was proposed to measu re the phase retardation for many kinds of wave-plates whose axes were unknown. The stepping motor was used to drive the wave-plate and a grating encoder was used to measure rotating angle of the analyzer.A light intensity meter was used to gather the energy of laser.While the measured wave-plate was rotated around,the phase retardation was obtained from the maximum and minimum value.This method is rapid and convenient.