To study the narrow fan beam computed tomography (CT) reconstruction algorithm, there must be CT projections of the tested object. CT experiment is costly, whereas CT simulation is economic. Considering the characteristic of narrow fan beam CT, we establish formulas of narrow fan beam CT projections. Reconstruction of narrow fan beam CT projections was carried out with rebinning algorithm to prove the effectiveness of our algorithm. Result shows that our algorithm works well. The method can also be applied to the computation of parallel beam CT projections and wide fan beam CT projections.