With the emergence of HDTV, the application of aspect ratio conversion (ARC) is getting wider in related fields. In this paper, a new aspect ratio conversion algorithm is proposed based on human visual perception. To start with, the fuzzy cluster algorithm based on the modified partition fuzzy degree algorithm is applied to cluster motion vectors adaptively, and then the image motion center of gravity (MCOG) is estimated based on the clustering result. Moreover, to solve the dithering artifact, a splitting region approach based on MCOG and center region of image is developed. Finally, different regions of image are scaled with different ratios. Experimental results illustrate that the proposed method has good consistency with the human visual perception and show its superiority.