In order to satisfy the demand of the measurement for reflection phase retardation with high precision in a short time, a measuring system based on the typical optical structure which is composed of polarizer, prism and analyzer (PPA) is presented. By means of least-squares method, a binary linear analysis is employed to fit the intensity distribution points which are captured without knowing the initial analyzer angle. Then, two sets of intensity distribution points captured under the different conditions of polarizing angle are processed with the methods of repeated fitting and approximation to obtain an intersection, which is just the measured value of reflection phase retardation. In this approach, data collection of the intensity distribution as well as the associated numerical calculation can be performed via software system without setting optical elements′ azimuth accurately. Moreover, all of the measuring operations can be completed in 15 s. The experimental results show the error of the measured result of reflection phase retardation is 0.005 rad and the repeatability of which is 0.0016 rad as well.