The clustering methods based on Fuzzy C-Means (FCM) are frequently used in image-segmentation. But the standard FCM algorithm has some defects, especially ignoring the pixel spatial information's influence on the classification result. For the sake of a more reasonable objective function, an improved FCM algorithm is proposed in this paper, which uses spatial information and S-function to determine the weight coefficients of the objective function. Experimental results show that the proposed algorithm has better performance than the standard FCM algorithm.