Catalytically　active　metals　atomically　dispersed　on　supports　presents　the　ultimate　atom　utilization　efficiency　and　cost-effective　pathway　for　electrocatalyst　design.　Optimizing　the　coordination　nature　of　metal　atoms　represents　the　advanced　strategy　for　enhancing　the　catalytic　activity　and　the　selectivity　of　single-atom　catalysts　(SACs).　Here,　we　designed　a　transition-metal　based　sulfide-Ni3S2　with　abundant　exposed　Ni　vacancies　created　by　the　interaction　between　chloride　ions　and　the　functional　groups　on　the　surface　of　Ni3S2　for　the　anchoring　of　atomically　dispersed　Pt　(Pt-SA-Ni3S2).　The　theoretical　calculation　reveals　that　unique　Pt-Ni3S2　support　interaction　increases　the　d　orbital　electron　occupation　at　the　Fermi　level　and　leads　to　a　shift-down　of　the　d　-band　center,　which　energetically　enhances　H2O　adsorption　and　provides　the　optimum　H　binding　sites.　Introducing　Pt　into　Ni　position　in　Ni3S2　system　can　efficiently　enhance　electronic　field　distribution　and　construct　a　metallic-state　feature　on　the　Pt　sites　by　the　orbital　hybridization　between　S-3p　and　Pt-5d　for　improved　reaction　kinetics.　Finally,　the　fabricated　Pt-SA-Ni3S2　SAC　is　supported　by　Ag　nanowires　network　to　construct　a　seamless　conductive　three-dimensional　(3D)　nanostructure　(Pt-SA-Ni3S2@Ag　NWs),　and　the　developed　catalyst　shows　an　extremely　great　mass　activity　of　7.6　A　mg(-1)　with　27-time　higher　than　the　commercial　Pt/C　HER　catalyst.