This work employed an unconventional sol–gel/fast precipitation method following annealing at 450 °C to prepare oxygen vacancy-engineered Cu-doped TiO2 nanoparticles (Cu-TiO2-n, n = 0, 2, 4, 6, 8, 10 %) for photocatalytic hydrogen evolution (PHE) reaction. Adding Cu in the precursor stage for preparing Cu-TiO2-6 with optimized electrochemical effect and energy band structure realizes the PHE performance on highly defective TiO2 with optimized oxygen vacancies (VO). The VO in Cu-TiO2-6 acts as the O-trapping sites to facilitate proton formation for PHE to achieve 2770 μmol/g·h under a 150 W xenon lamp. The challenge of further improving the PHE rate of the highly defective Cu-TiO2-6 is overcome by a thermally reduced instead of photo-reduced Pt deposition with a PHE rate of 4934 μmol/g·h. A kinetic reaction micromechanism combined with the band structure is proposed to understand the hidden PHE explanation.