For semiconductor nanocomposite systems,there are usually a large number of defects such as points and surfaces,due to the lattice mismatch of different components and interface pollution.Especially,the interface defects seriously affect the carrier interface transport process,thus significantly inhibiting its photoelectric conversion performance.The composite system of photocatalyst graphite nitride carbon (C3N4)and transition metal phosphide (CoP)is taking as research material．Interface optimization of C3N4/CoPx using L-Cys molecular bridging ligand to enhance photocatalytic hydrogen production activity.C3N4 nanosheets were prepared by hot polymerized urea/melamine mixture.C-SH bond and C3N4were covalently bonded by L-Cys molecular sensitization,and Ｒ-C3N4/CoPx was prepared by photodeposition loaded with CoPx nanoparticles (NPs).The results show that the —COO－ and —NH2 functional groups of L-Cys are covalent with Co and P atoms of CoPx NPs respectively. The influence of L-Cys bridging ligand on the electron interface transfer behavior of Ｒ-C3N4/CoPx was investigated by time-resolved fluorescence spectroscopy and electrochemical tests.The results showed that the introduction of L-Cys bridging ligand could halve the fluorescence lifetime of R-C3N4/CoPx,reduce the electron transfer impedance by one order of magnitude,and improve the surface charge transfer efficiency by nearly 16%.Thus,the Ｒ-C3N4/Co x photocatalytic hydrogen evolution rate increased by 16.5 times.