The development of catalysts with enhanced photocatalytic performance has been receiving growing attention in recent years. The performance of heterostructural catalysts can be dependent on the interface structures of heterostructure. Through a mechanical-chemical pre-reaction, Pt and Au ions are anchored onto red g-C3N4 nanosheets to control the in-situ growth of Pt and Au clusters during thermal polymerization process. Electron spin resonance analysis confirms the formation of Z-scheme heterostructure. The Z-scheme heterostructures consisted of Pt/Au clusters and superior thin red/yellow g-C3N4 nanosheets are created with enhanced photo-chemical activity. The homogeneous distribution of Pt/Au clusters and the formation of Z-scheme heterostructure are the keys in improving the photocatalytic activities of the material. The estimated H2, CO, and CH4 evolution rate of Pt immobilized composites with optimized Pt loading are 5057, 4.82, 1.56 μmol/g/h, respectively. The remarkably enhanced photocatalytic performance of Pt clusters incorporated g-C3N4 samples is due to the formation of Z-scheme heterostructures which improves the photogenerated charge carrier transport. Enhancement in photocatalytic activity is also observed for Au clusters embeded g-C3N4 nanosheets. The results provide important platforms for exploiting highly efficient catalysts.