An accurate measurement method of the polarized light′s phase retardation based on the crystal wedge is introduced, and is applied to measure the phase retardation′s temperature dependence of the zero- and multiple-order quartz wave plates. The measured results are insensitive to the power fluctuation of the light source, and the accuracy of the phase measurement can reach 0.05°. Compared to the traditional phase measurement, there is no adjustment of any optical components during the crystal wedge′s experiments, the on-line phase detection can be realized. This method can be used at the phase retardation measurement of any optical components, or at the various optical wavelengths.