In　this　work,　a　novel　and　facile　sequential　cation-exchanging　strategy　was　developed　to　synthesize　phosphorus　doped　g-C3N4　nanotubes,　and　resulted　nanotubes　were　composed　of　small　nanorods　with　length　of　several　hundred　nanometers.　Obtained　products　exhibit　greatly　enhanced　photocatalytic　hydrogen　evolution　with　rate　of　4.59　mmol　h(-1)　g(-1),　which　is　16　times　higher　than　that　of　the　bulk　g-C3N4　under　visible　light　irradiation.　Mechanistic　investigation　reveals　that　the　superior　photocatalytic　property　could　be　attributed　to　its　improved　visible　light　absorbance,　well　suppressed　charges　recombination　and　nanostructural　construction.