Conventional　photosensitizer-based　photodynamic　therapy　is　triggered　by　UV-light　irradiation　and　depends　on　oxygen.　However,　it　is　hard　to　be　applied　to　the　deep　and　hypoxic　tumor.　To　address　this　issue,　we　reported　a　new　kind　of　g-C3N4　nanosheet　decorated　with　gold　nanoparticles　(AuNPs),　which　could　generate　a　high　amount　of　reactive　oxygen　species　(ROS)　under　a　670　nm　laser　irradiation　in　an　oxygen-free　environment.　This　synthesized　semiconductor-metal　heterojunction　served　as　a　superior　photodynamic　agent,　showing　prominent　cancer　cell-killing　and　tumor　growth-suppressing　effects　in　the　presence　of　a　670　nm　light　and　g-C3N4-AuNP　composites,　and　its　excellent　ROS　generation　property　was　also　validated　by　further　bactericidal　experiment.　©　2019　American　Chemical　Society.