A novel V-doped CeO2-supported alkali-activated-steel-slag-based catalyst (V-CeO2/AC) for photocatalytic decomposition of water to hydrogen was prepared via co-impregnation method. The chemical composition, mineral phase, morphology, and optical performances of the synthesized catalyst samples were characterized by XRF, XRD, SEM, UV-Vis DRS, and so on. XRD and SEM results show that calcium silicate hydrate (Ca1.5SiO3.5·xH2O) mineral phase is formed in the carrier sample, and the prepared catalyst specimens are made up of approximately 50 nm particles. After 6 hours of xenon lamp irradiation, the catalyst supported on V-doped 8wt％ CeO2 exhibits the highest photocatalytic hydrogen production activity (8292 μmol/g), which is attributed to the interaction between the V-doped CeO2 active components and FeO existed in catalyst carrier. A possible photocatalytic decomposition of water for hydrogen production mechanism over the V-8CeO2/AC catalyst was proposed.