Electrocatalytic　full　water　splitting　is　still　a　challenge.　Porous　single　-crystalline　(PSC)　has　a　long-range　ordered　crystal　structure　and　large　specific　surface　area,　which　has　great　potential　to　be　applied　in　the　fields　of　catalysis　and　energy　storage.　Nitride　single　-crystalline　possesses　unsaturated　coordination　of　metal　-nitrogen　active　sites　on　the　crystal　surface,　which　has　shown　excellent　performance　in　the　electrocatalytic　field.　PSC　tungsten　nitride　mesoporous　nanosheets　are　grown　from　single　-crystalline　(SC)　WO3　nanosheets　and　are　applied　as　bifunctional　electrocatalysts　in　Hydrogen　Evolution　Reaction　(HER)　and　Oxygen　Evolution　Reaction　(OER).　The　overpotential　of　mesoporous　W2N　and　WN　single　-crystalline　nanosheets　in　HER　is　as　low　as　67.44　mV　and　84.26　mV　at　a　current　density　of　10　mA　cm　-2,　respectively.　A　low　overpotential　has　been　found　in　PSC　W2N　and　WN　as　the　OER　electrocatalyst.　The　PSC　tungsten　nitride　mesoporous　nanosheets　provide　a　simple　and　effective　solution　for　efficient　water　splitting　electrocatalysts.