An image segmentation algorithm is proposed in this paper to display digital elevation model(DEM) image with colors which occupy respectively an approximately equal area in display window.Firstly,the data set is classified into many groups according to elevation values;secondly,the groups adjacent with few data points are combined,when each group has approximately equal number of data points,and their limits are taken as the thresholds.The results of experiment and analysis show that the algorithm is efficient as well as time- and space-saving.