C3N　has　attracted　much　attention　as　an　anode　material　for　lithium-ion　(Li-ion)　batteries,　owing　to　its　excellent　mechanical　and　electronic　properties.　However,　its　weak　Li　adsorption　strength　and　mobility　have　limited　its　further　application.　Phosphorene　(P)　exhibits　a　high　bonding　strength　with　Li　and　excellent　Li-ion　mobility,　but　low　stiffness.　Thus,　we　propose　that　constructing　a　C3N/P　hybrid　material　will　not　only　negate　the　deficiency　of　C3N　but　also　result　in　a　new　high　performance　electrode　material.　A　C3N/P　heterostructure　is　constructed　and　studied　by　first-principles　calculations.　This　heterostructure　exhibits　an　excellent　stiffness　(Young＇s　modulus　is　448.32　N　m(-1)),　which　is　even　better　than　that　of　graphene.　The　bonding　strength　of　Li　inserted　into　the　intralayer　of　the　C3N/P　heterostructure　(1.78-2.02　eV)　is　much　higher　than　that　in　pristine　monolayer　C3N　(0.32　eV)　and　phosphorene　(1.67　eV).　Moreover,　the　C3N/P　heterostructure　shows　a　high　capacity　of　468.34　mA　h　g(-1),　and　better　conductivities　of　electricity　and　ions　than　pristine　monolayer　C3N.　The　excellent　mechanical　properties,　high　capacity,　good　conductivities　of　electrons　and　ions　and　moderately　high　bonding　energy　indicate　that　the　C3N/P　heterostructure　is　a　promising　anode　material　for　lithium-ion　batteries.