The　band　gap　of　hexagonal　boron　nitride　(h-BN)　is　far　too　wide　for　efficiently　utilizing　visible　light,　limiting　its　application　in　photocatalysis.　The　present　study　employs　first　principles　calculations　to　demonstrate　that　the　band　gap　energies　of　porous　h-BN　(p-BN)　can　be　tuned　by　carbon　doping　to　levels　appropriate　for　the　absorption　of　visible-light,　and　that　the　conduction　band　and　valence　band　match　well　with　the　potentials　of　both　hydrogen　and　oxygen　evolution　reactions.　Importantly,　a　strategy　of　carbon　doping　to　improve　the　energy　level　of　valence　band　maximum　is　also　proposed.　Moreover,　the　carbon-doped　p-BN　exhibits　good　separation　between　photogenerated　electrons/holes　and　structural　stability　at　high　temperatures.　The　DFT　results　help　the　design　of　high-performance　two-dimensional　photocatalysts　that　avoid　the　use　of　metals.