Graphene,　having　all　atoms　on　its　surface,　is　favorable　to　extend　the　functions　by　introducing　the　spin-　orbit　coupling　and　magnetism　through　proximity　effect.　Here,　we　report　the　tunable　interfacial　exchange　field　produced　by　proximity　coupling　in　graphene/BiFeO3　heterostructures.　The　exchange　field　has　a　notable　dependence　with　external　magnetic　field,　and　it　is　much　larger　under　negative　magnetic　field　than　that　under　positive　magnetic　field.　For　negative　external　magnetic　field,　interfacial　exchange　coupling　gives　rise　to　evident　spin　splitting　for　N　not　equal　0　Landau　levels　and　a　quantum　Hall　metal　state　for　N　=　0　Landau　level.　Our　findings　suggest　graphene/BiFeO3　heterostructures　are　promising　for　spintronics.