The 0-2π vortex phase plate is introduced to measure the phase retardance of the wave plate. By constructing a functional relationship between the phase delay of the wave plate and the azimuth angle of the hollow elliptical spot of the emitted light, the phase delay is simulated and calculated. Furthermore, the demonstration and analysis of the wave plate test method are realized. Theoretically, the measurement range of the phase retardance of the wave plate is expanded to 270°, and the theoretical measurement error does not exceed ±0.71%.