Abstract: Peak-to-Valley departure (PV) is a widely used parameter in evaluating the quality of optical surface and wavefront. However, there is great uncertainty in optical surface testing using high resolution interferometer. In order to evaluate the quality of optical surface and wavefront more precisely, PV20, PVr and PVq are discussed. Through numerical simulation and experiment, it is proved that these three parameters can not only represent the real optical surface, but also be insensitive to interferometer spatial resolution. In addition, they have great advantage in metrology repeatability, hence, PV20, PVr and PVq are better than PV for characterizing optical surface.