Photocatalytic hydrogen production coupled with selective oxidation of organic substances is of significance and remains a grand challenge because of unsatisfied photocatalytic activity and unclear mechanism. Herein, we first design and synthesize atomically dispersed Pd on ZnIn₂S₄ (PdSA-ZIS) for simultaneously photocatalytic hydrogen production and oxidation of benzylamine. Based on systematic characterization with a combination of theoretical simulations, light irradiation-kelvin probe force microscopy (KPFM) and time-resolved photoluminescence spectrum etc, we demonstrate that Pd single atoms can modulate charge polarization as well as the active sites of ZnIn₂S₄ to promote spatial charge separation and decrease the energy barriers of reaction. The electrons are enriched around Pd single atoms-ZnS layer with lowest energy barriers of H2 production, while more holes are accumulated on InS2 layer for dehydrogenation of benzylamine. This enables PdSA-ZIS to exhibit remarkable photocatalytic performance for the co-production of N-benzylidenebenzylamine (10.2 mmol g⁻¹ h⁻¹) with selectivity of 100% and H₂ (11.1 mmol g⁻¹ h⁻¹) under visible irradiation. Furthermore, by means of controlled experiments, theoretical simulations and in situ electron spin resonance (ESR) spectroscopy, a synergetic photocatalytic redox mechanism on the Pd single atom-ZIS interface for dehydrogenation and coupling of benzylamine and H₂ production has been investigated in detail.