Abstract: Interferometric synthetic aperture radar (InSAR) measures the height of the object based on the distance difference reflected by the absolute phase difference of the corresponding pixels on two pieces of synthetic aperture radar (SAR). But in fact the phase difference is restricted to (-π,π), which causes phase wrap. The branch-cut method is one of the most important approaches for the phase unwrapping. In this paper, an improved branch-cut algorithm is proposed based on the Goldstein algorithm. The positive and the negative residues in the interference image are combined in this algorithm and then re-combined and replaced by using the length of the branch-cut as criteria so that the overall length of the branch-cut can be reduced gradually and the "isolated island phenomenon" in the unwrapping process can be overcome effectively. The proposed method has been verified through both the simulated and experimental data.