Abstract: Phase unwrapping for interferogram is the key and the most difficult step in the processing of Interferometric Synthetic Aperture Radar. By using the fringe lines of the interferometric phase image, we present one phase unwrapping algorithm based on region block. The image is first divided into distinct blocks. Blocks are delimitated by fringes lines and the border of the image such that there is no phase jump inside each of the blocks. Then phase unwrapping is performed block by block over the whole image. Finally, post-processing is applied to remove local error due to incorrect unwrapping. Results are shown on the real and simulated data. Comparison with one of the traditional methods demonstrates the efficiency and robustness of the approach.