A CdS/H2Ti5O11 ultrathin nanobelt nanocomposite (CdTi) was fabricated successfully by a two-step process. It was confirmed by SEM and TEM/HRTEM that the highly dispersed CdS about 15 nm was firmly anchored on the ultrathin nanobelt. The as-prepared CdTi-5 with an optimal loading of 81.3% CdS converted 4-nitroaniline to p-phenylenediamine almost 100% with a selectivity of about 98% in 3 min under visible light irradiation. Its photocatalytic activity was much higher than that of the bare CdS and P25/CdS composition. The highly efficient performance was attributed to the synergetic effects of the formed heterojunction between titanate nanobelt and CdS as well as the unique features of the titanate nanobelt, which makes the photo-generated electron transfer smoothly and promotes the separation of photo-induced carriers. Finally, based on the experimental results of Mott-Schottky, UV-vis DRS and EPR, a possible reaction mechanism for the hydrogenation of 4-nitroaniline over the CdTi was proposed.