The clustering number needs to be determined artificially when image segmentation using FCM is per-formed.In order to solve this problem,an improved algorithm based on FCM is proposed.In this algorithm,first,a sub- image decomposition of the ori- ginal image is conducted on the basis of quad- tree structure,by which theoriginal image is divided into 2 ×2 sub- images equally and each sub- image is divided into 2 ×2 sub- images equallyagain until the sub- image satiates certain conditions.Then,the sub- image is segmented by using FCM with theclustering number 2.Moreover,region merging is carried out according to the region area and the Bhattacharyyadistance of two adjacent regions’histogram,with the segmentation results being finally obtained without determi-ning the clustering number directly.Experimental results indicate that the proposed algorithm possesses good seg-mentation effectiveness,and that,to some extent,the computation complexity is reduced,because the segmenta-tion using FCM helps reduce the number of samples for each clustering.