The algebraic reconstruction technique (ART) is a classical iterative image reconstruction algorithm, which is suit for image reconstruction from incomplete projection data. In order to improve the image reconstruction quality of MART (Multiplicative ART), this paper presents an image reconstruction method based on sub-pixel. Firstly, we equally decompose each pixel of original image into four sub-pixels. Then we present a fast intersection algorithm of ray-pixel to calculate weight coefficients and index of sub-pixel. The reconstructed high resolution image is obtained using MART, from which we can obtain the high quality reconstruction image with original resolution by merging sub-pixels. Experimental result shows that the proposed method is very effective, compared with traditional method, we can get a reconstruction speedup over 3 times and improve the reconstructed image quality obviously.