Abstract: Fan beam industrial CT system usually adopts filter back-projection algorithm to reconstruct CT images. Its computational complexity is O(N³). The running speed of this algorithm, without being optimized, can抰 meet the speed requirement of industrial testing. Following the summary of these optimization steps done by us, an optimizing method based on the features of sine and cosine functions is discussed chiefly. Analysis shows that the reconstruction speed can be improved three times by adopting this method. Computer simulations demonstrate that the running speed in practice can be improved more than six times if this method cooperates with other optimization methods.