In situformation of p-n heterojunctions between TiO₂and Cu_xO in heteroatom-doped carbon nanocomposites and their applications in photocatalytic H₂evolution were demonstrated. One-step pyrolysis of bimetal-organic-frameworks NH₂-MIL-125(Ti/Cu) in steam at 700 °C forms a p-n heterojunction between TiO₂and Cu_xO nanoparticles. Concurrently, a phasejunction between nitrogen/carbon co-doped anatase and rutile TiO₂is formed, accompanied by the formation of Cu_xO heterostructures. These multi-heterostructures are embedded in N-containing and hydrophilic carboxyl functionalized carbon matrix. The optimized TiO₂/Cu_xO/C composite multi-heterostructures offer multiple pathways for photoinduced electrons and holes migration, absorb more visible light, and provide an increased number of active sites for photocatalytic reactions. Without loading expensive noble metals, the TiO₂/Cu_xO/C nanocomposite derived at 700 °C in steam exhibited a superior photocatalytic H₂generation activity of 3298 μmol g_cat⁻¹h⁻¹under UV-Visible light, 40 times higher than that of commercial TiO₂. This work offers a simple approach to fabricate novel photocatalytic nanocomposites for efficient H₂generation.