The　manipulation　of　central　atom　coordination　environments　can　greatly　boost　catalytic　performances　and　promote　the　understanding　of　associated　mechanisms　in　both　sub-nanometer　clusters　and　atomically　dispersed　catalysts.　In　this　study,　sub-nanometer　＂raft＂-like　PtNx　clusters　were　synthesized　on　a　TiO2　support,　and　the　significant　enhancement　effects　of　the　Pt-N　coordination　structure　on　the　performance　of　hydrogen　evolution　reaction　(HER)　are　demonstrated.　In　acidic　media,　the　PtNx　catalyst　display　a　superior　HER　activity　(37.5　A　mg(-1)　Pt)　and　turnover　frequencies　(37.9H(2)　s(-1))　at　overpotential　of　50　mV;　outperforming　commercial　Pt/C　by　a　factor　of　13.3　and　3.9,　respectively.　Density　functional　theory　(DFT)　calculation　results　reveal　that　the　charge　transfer　occur　from　the　N　to　the　neighboring　Pt　atoms　when　the　hydrogen　is　adsorbed　on　N　atoms;　such　a　charge　redistribution　within　Pt-N　coordination　structure　leads　to　a　smaller　H*　free　energies　on　the　activated　N　atoms,　and　is　believed　to　account　for　the　higher　HER　activity.