According to the birefringence dispersion character of a quartz crystal, the theoretical analysis and numerical simulation about the polarization interference spectrum are given,and then a systematic way of measuring the phase retardation and thickness of the quartz wave plate, which is based on the principle of polarization interferometry, is put forward. With the polarization interference spectrum, the phase retardation of quartz wave plates can be determined at a wide spectral range from 200～2000 nm. Through accurate judgment of extreme points of the polarization interference spectrum at long-wave band, the physical thickness of the quartz wave plate can also be achieved exactly. Experimentally, the polarization interference spectrum of a quartz wave plate is measured with Lambda 900 UV/VIS/NIR spectrophotometer. Under the conditian of 0.1 nm wavelength resolution, the thickness accuracy is 0.1 μm. The result of error analysis shows that the relative error can be reduced efficiently by use of spectrometers with higher spectral resolution and longer spectral band to measure and calculate.