Photocatalysis　is　a　promising　energy　conversion　and　environmental　restoration　technology.　The　main　focus　of　photocatalysis　is　the　development　and　manufacture　of　highly　efficient　photocatalysts.　Semiconductor-based　photocatalysis　technology　based　on　harnessing　solar　energy　is　considered　as　an　attractive　approach　to　solve　the　problems　of　global　energy　shortage　and　environmental　pollution.　Since　2009　pioneering　work　has　been　carried　out　on　polymeric　carbon　nitride　(PCN)　for　visible　photocatalytic　water　splitting,　thus　PCN-based　photocatalysis　has　become　a　hot　research　topic,　demanding　significant　research　attention.　This　article　reviews　the　physical　and　chemical　properties,　synthesis　methods,　and　the　methods　to　control　the　morphology,　heteroatom　doping,　and　construction　of　heterojunctions　to　improve　the　performance　of　PCN-based　photocatalysts　in　water　splitting　and　nitrogen　fixation.　Through　different　design　strategies,　the　photo-generated　electron-hole　pair　separation　efficiency　of　PCN　materials　can　be　effectively　improved,　thereby　improving　their　photocatalytic　performance.　Finally,　the　challenges　of　PCN-based　photocatalysts　in　water　splitting　and　nitrogen　fixation　applications　are　discussed　herein.　It　is　strongly　believed　that　through　different　design　strategies,　efficient　PCN-based　photocatalysts　can　be　constructed　for　both　water　splitting　and　nitrogen　reduction.　These　excellent　modification　strategies　can　be　used　as　a　guiding　theory　for　photocatalytic　reactions　of　other　promising　catalysts　and　further　promote　the　development　of　photocatalysis.