In order to increase the accuracy of the phase unwrapping algorithm based on image segmentation and merging, an improved algorithm based on existing algorithm is proposed. The method of unequal region segmentation is taken to make the regional information complete and accurate reproduction. For different regions with noise and under sampling conditions, different phase unwrapping algorithms are taken respectively. A weighted stack approach to improve the accuracy of the phase unwrapping results of merging the overlapping region of the block is presented. Simulation and measurement are taken to test the improved algorithm. The results show that the improved algorithm recovers the phase information of the measured object more accurately and faster. It is not only suitable for dealing with the phase unwrapping of large interferogram, but also for dealing with the wrapped phase which has areas with too dense stripes.