Abstract: Image reconstruction is a mathematic process which reconstructs three-dimensional volume data from two-dimensional projections.Numerical simulation is always used to study the characteristics of some reconstruction algorithm,in which projection simulation of some numerical phantom is the first step.The Shepp-Logan phantom is the most widely used in the field of Computed Tomography(CT).In this paper,parameters of the three-dimensional Shepp-Logan phantom and its modified forms are introduced firstly.Secondly,a projection simulation method of the three-dimensional Shepp-Logan phantom on general scan trajectory is presented.Thirdly,projections of the three-dimensional Shepp-Logan phantom in circular and helical scans are simulated using the proposed method.Then,the FDK algorithm and helical-FDK algorithm are employed to deal with these projections,respectively.Experimental results show that the mean square errors between the reconstructed images and numerical phantoms are both less than 2‰,and indicate that the presented method has higher accuracy.