Objective To reduce the interface roughness of the Ni /Ti multilayer film, and improve the neutron reflectivity of the multilayer. Methods A series of Ni /Ti periodic multilayers were fabricated by the ion beam assisted deposition device, and the Ni / Ti multilayers were rinsed and polished though bombarding by ion beam with different ion energy and polishing time. The Ni /Ti multilayers was deposited by the reactive sputtering, the argon gas mixed with hydrogen was used as the working gas when the Ti layers were deposited to embed the hydrogen atom into the Ti layers, which can change the grain structure and affect the interface state of Ni /Ti multilayers. Results With the increase of the assisted ion source忆s power, the surface roughness of the Ni /Ti multilayer films was increased. And under appropriate ion energy condition, with the bombardment time getting longer, the surface roughness of the Ni /Ti multilayers was reduced, the surface roughness of the Ni /Ti multilayers films became smaller and the interfaces got more distinct when the H atoms were embedded into the Ti layers. Conclusion The interface state of the multilayer films can get better when impacted by the lower energy ion beam with the suitable time of polishing. The hydrogen atom in the Ti crystal lattice can suppress the diffusion between the Ni and Ti layers, and reduce the grain size thus suppressing the increase in the interface roughness.