In the study, we successfully conducted vanadium doping to improve photocatalytic performance of the CuWO4 for water splitting to produce hydrogen. The doping mechanism, optimal doping ratio and material stability were investigated by various characterization methods and water splitting experiments. We found that the V substituted several W elements of the CuWO4 crystal. In the V-CuWO4, V dopant existed in form of the V5+, which created new energy level between the conduction band (CB) and the valence band (VB) of the CuWO4 to improve charge transfer as well as to prevent the e(-) and h(+) recombination of the material. The substitution of W by V dopant also led the formation of Cu+ and W5+ in the CuWO4 crystal. The formation of Cu+ and W5+ in the CuWO4 crystal not only narrowed the energy band gap but also increased the CB potential of the material. Therefore, the V-CuWO4 generated significant amount of e(-) under visible light and the generated e(-) was strong enough to react with H+ to produce H-2. The optimal V/W ratio for maximum improving photocatalytic performance of the CuWO4 was 6 wt%. Finally, we investigated that our prepared V-CuWO4 showed high stability during long-term water splitting process. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.