In order to gain the phase retardation and birefringence of mica wave plate according to the increase of the wavelength, the phase retardation of the mica wave plate is measured continuously in the spectral region of 400~770 nm using a spectroscopic ellipsometer. After the calibration of the mica plate, the experimental data are collected by the detector and sent to the computer. From the outputted data, the retardation can be obtained according to the increase of the wavelength. With the measured phase retardation, the birefringence of the mica wave plate can be calculated. The birefringence dispersion curve and dispersion formula are also gained. The proposed method can measure a mica wave plate with arbitrary phase retardation and has the merits of convenient, quick and high accuracy.