This paper brings forward a new method which can measure the phase delay and mark the placement of the fast and slow axis of wave plate at the same time. The measured wave plate is placed between polarizer and analyzer, and uniformly revolves under the control of stepping motor drived by computer. The curve of emergent light intensity vs time is obtained through continuous measuring the emergent light intensity. The phase delay can be calculated and the placement of the fast and slow axis of the wave plate can be marked after analyzing the curve. The process of experiment is controlled by computer, so the manipulation is sample, further more, it can avoid error originated from the limit of eyes′distinguishability and the inaccuracy of manual regulation, as a result, it has high degree of accuracy.