Abstract: Phase unwrapping is one of the key steps for the processing of InSAR data. The quality of the unwrapping results affects the final DEM (Digital Elevation Model) directly. In this paper, a new quality map is proposed. This new quality map reduces the affluence of the slope effect by plane-fitting and is denoted by the variance between the fitted plane and the original data. Also, an improved phase unwrapping method with a quality map is introduced in this paper. This new technique simplifies the route-searching processes by setting up a look-up table, which reduces the total processing time greatly. The experiment results with real InSAR data show that the proposed method is correct and effective.