Abstract: Algebraic Reconstruction Technique is an important method for image reconstruction. To improve the reconstruction speed of ART, this paper presents a new and fast algorithm to calculate projection coefficient based on different situations of grids intercepted by ray. This Algorithm can calculate the projection coefficient by simple operation such as addition, subtraction and comparison. Since the computation of intersection and sorting in traditional algorithms are avoided, the reconstruction speed is greatly increased. The experiments using Shepp-Logan phanom show that the new algorithm is more effective than the traditional algorithms.