Abstract: ART is one of significant and classical methods in CT reconstruction. Relaxation factor is an important parameter of ART. In this article, effect of relaxation factor on convergence speed and quality of reconstructed images has been researched, using the projections obtained from Cold Neutron CT facility of Mianyang Research Reactor, A chosen range of relaxation factor is given considering reconstruction efficiency and image quality, which has an important reference to neutron CT reconstruction.