Two-dimensional　single-layer　C3N　has　attracted　extensive　attentions　currently　owing　to　its　excellent　mechanical　and　electronic　properties.　In　this　work,　as　a　potential　anode　material　in　lithium-ion　battery,　the　pristine　and　defect-containing　C3N　are　systematically　studied　base　on　first-principles　calculations.　The　results　show　pristine　C3N　might　has　great　potential　in　the　application　of　lithium-ion　batteries　due　to　its　excellent　stiffness　(Young＇s　modulus　is　364.33　N　m(-1)),　high　storage　capacity　(1071.56　mA　h　g(-1)),　good　electronic　conductivity　(bandgap　is　0.39　eV),　and　lithium　migration　capability　(energy　barrier　is　0.27　eV).　We　further　investigate　the　adsorption　and　diffusion　mechanisms　of　lithium　ion　in　C3N　with　and　without　vacancy　defect　and　find　out　as　an　anode　material,　it　is　vital　to　control　defects　of　C3N　to　improve　the　performance　of　lithium　ion　batteries.　These　studies　could　deepen　the　understanding　of　perfect　and　defect-containing　two-dimensional　materials　and　provide　a　guidance　for　the　application　of　CN-based　material　in　lithium-ion　batteries.