SrTiO3 is a promising material for the photoelectrochemical (PEC) cathodic protection technology due to its intrinsic band structure. Its disadvantage of light absorption only in the ultraviolet region can be effectively solved by Cr doping. The Cr dopant usually exists as two states of Cr3+ and Cr6+, among which the latter one usually behaves as the trapping center for the photoinduced electrons and leads to the decrease of the PEC performance. In this paper, a hydrogen treatment process is performed on the Cr-doped SrTiO3 to reduce the Cr6+. It is verified that hydrogen treatment reduces Cr6+ to Cr3+, leading to the increase of the concentration of the charge carriers and the decrease of the charge transfer resistance. And also, hydrogen treatment induces the formation of oxygen vacancy, which leads to the negative shift of conduction band potential and the increase of the concentration of the charge carriers. The effect of the hydrogen treatment temperature is further studied in this work. Higher temperature will promote the reduction degree of Cr6+ and increase the concentration of oxygen vacancy. However, hydrogen treatment with excessively high temperature will induce too high concentration of oxygen vacancy, which would act as the recombination centers of the photogenerated charge carriers, suppress the mobility conduction and thus lead to the decrease of the PEC performance. Therefore, benefiting from the Cr6+ reduction and modification with appropriate concentration of oxygen vacancy, the Cr-doped SrTiO3 with hydrogen treatment at 250 degrees C shows the optimal PEC cathodic protection performance in NaCl solution. (C) 2019 Elsevier Ltd. All rights reserved.