Defects　play　a　significant　part　in　promoting　photocatalytic　activity　for　H-2　production.　Various　methods　such　as　chemical　reduction　have　been　performed　to　metal　oxide　based　photocatalysts.　Herein,　we　present　the　NaBH4　reduction　route　to　introduce　the　defects　into　the　graphitic　carbon　nitride　(g-C3N4)　to　enhance　photocatalytic　activity.　A　new　-C　N　group　is　observed　in　the　FTIR　spectra　of　treated　g-C3N4　nanosheets　indicating　the　presence　of　structural　defects.　At　the　same　time,　the　B　signal　appears　in　the　X-ray　photoelectron　spectroscopy　analysis,　suggesting　that　B　is　doped　in　the　g-C3N4　during　the　treatment.　All　these　results　manifested　that　multiple　types　of　defects　are　introduced　in　the　g-C3N4　during　the　NaBH4　treatment.　The　UV-vis　spectra　illustrate　that　the　absorption　band　edge　of　g-C3N4　is　extended　from　420　to　450　nm　after　NaBH4　treatment.　This　demonstrates　that　the　band　gap　of　g-C3N4　turns　narrow　owing　to　the　introduction　of　defects.　Photocatalytic　H-2　production　of　defective　g-C3N4　is,-5-fold　better　than　that　of　pristine　g-C3N4.　To　understand　the　enhanced　mechanism,　the　apparent　quantum　efficiency,　photoluminescent　spectra,　transient　photocurrent　and　electrochemical　impedance　spectra　are　investigated.　The　results　show　that　the　charge　separation　efficiency　is　greatly　strengthened　in　the　defective　g-C3N4.　Upon　these　findings,　the　enhancement　of　catalytic　activity　can　be　attributed　to　both　the　broad　light　adsorption　range　and　highly　efficient　charge　separation　process.