Alpha-expansion algorithm based on Graph Cuts is a useful method for minimizing energy function established by Markov Random Field model of image segmentation. However, the number of edge of the graph constructed by the algorithm is large, so the speed is rather slow. In order to reduce the complexity of the alpha-expansion algorithm, the relationship between the pixels labeled alpha and pixels labeled non-alpha was only considered and the relationship between the pixels labeled non-alpha was omitted. This idea avoided adding auxiliary nodes which were one of main factor to affect the efficiency of the alpha-expansion algorithm. Since the constraints on the relationship between pixels set labeled different non-alpha was loosed，it was easier for the new algorithm to escape some local minimum of energy function so as to gain more optimal segmentation results. In experiments, compared with the standard algorithms based on Graph cuts, the algorithm had the better performance in the running time and the minimum energy.