Single atom catalysts (SACs) have an extremely high atom utilization and distinctive structures and properties in the field of photocatalysis. However, the premise of conducting scientific research and applications is still the stability and catalytic activity of single atoms on suitable substrates. Metal organic frameworks (MOFs), as one of the most suitable single-atom substrates, have tunable internal structures, unsaturated coordination bonds, and high specific surface areas. In this work, Ti-based MOF, MIL-125, was adopted as the precursor to prepare mesoporous Cu-loaded TiO2. During the synthesis of MIL-125, a Cu source was added, and Cu atoms were fixed by partly replacing Ti atoms in the Ti-O octahedron to coordinate with O atoms, resulting in a good dispersity, good stability and high loading amount. Experimental investigations demonstrated that dispersed Cu single atoms act as reaction centres, besides being able to accelerate the transfer of photoelectrons. Under simulated sunlight, the H2 evolution rate of the optimum Cu-TiO2 sample reaches 17.77 mmol g-1 h-1, nearly 101 times higher than that of the pure mesoporous TiO2. The apparent quantum efficiency (AQE) is 20.15% under 365 nm irradiation. This research opens a new thinking to preparing high stability and high activity single atom photocatalysts.