The role of metallic copper as a co-catalyst is still uncertain, which is an interesting problem in photocatalytic hydrogen evolution. There is debate over the role of Cu⁺, Cu²⁺ and metallic Cu during photocatalytic hydrogen generation. Herein, we identified that the metallic copper interlayer between Cu₂O and TiO₂ played a key role in the hydrogen evolution process. By fabricating the metallic Cu interlayer via in situ reduction of Cu₂O/TiO₂, efficient charge transfer took place over the Cu/Cu₂O/Cu/TiO₂ catalyst, while a retarded electron transfer was found over the Cu/TiO₂ catalyst. This interlayer structure provides a bridge for photoelectron transfer from th`e conduction band of TiO₂ to Cu₂O, significantly prolonging the life-time of electron transfer. In addition, the ratio of metallic Cu and Cu₂O could be easily adjusted by the loading amount of Cu₂O on TiO₂, and that the ratio affects the photocatalytic hydrogen evolution activity. A high transient photocurrent and long fluorescence lifetime (0.365 ns) were achieved over the Cu/Cu₂O/Cu/TiO₂ catalyst when the molar ratio of the interlayer metallic Cu to Cu₂O was 0.99. Under the same reaction conditions, the photocatalytic hydrogen generation activity of the Cu/Cu₂O/Cu/TiO₂ catalyst was three times than that observed with the Cu/TiO₂ catalyst with good stability.