The　design　of　stable　and　highly　efficient　photocatalysts　for　harmful　algae　removal　is　critical　to　preserve　the　aquatic　ecosystems.　In　this　work,　a　series　of　Ag2O/g-C3N4　with　p-n　heterojunction　were　synthesized　by　a　chemical　deposition　method　for　photocatalytic　algae　removal　under　visible　light.　The　effects　of　surface　charge　and　composition　ratio　for　the　formation　of　heterojunction　were　investigated.　The　crystal　phase,　functional　groups,　morphology,　optical　properties,　and　elemental　composition　of　the　synthesized　photocatalysts　were　also　characterized.　The　experimental　results　showed　that　the　photocatalytic　activity　of　14.3　wt%　Ag2O/g-C3N4　was　outstanding　for　algae　removal,　suggesting　that　the　bulk　graphitic　carbon　nitride　(g-C3N4)　with　negative　surface　charge　was　subject　to　combine　with　Ag2O　to　form　the　heterojunction.　In　addition,　the　photocatalytic　activity　of　the　heterojunction　was　greatly　affected　by　the　composition　ratio　of　synthesized　materials.　The　optimal　photocatalytic　activity　was　observed　when　the　composition　ratio　of　Ag2O　and　bulk　g-C3N4　was　1:6,　and　the　photocatalyst　reached　up　to　99.94　%　removal　of　Microcystis　aeruginosa　(M.　aeruginosa)　after　6　h　of　photocatalytic　reaction.　Superoxide　dismutase　(SOD)　and　malondialdehyde　(MDA)　of　algae　cells　decreased　while　catalase　(CAT)　increased　during　the　experimental　process.　Furthermore,　the　antioxidant　system　collapsed　and　algal　cell　membrane　was　ruptured　and　damaged,　resulting　in　the　release　of　a　large　number　of　important　ions　(e.g.,　K+,　Ca2+,　and　Mg2+),　the　decrease　of　chlorophyll　a　and　phycobiliprotein　(PB)　contents,　as　well　as　the　destruction　of　the　photosynthetic　system.　Overall,　the　synthesized　14.3　wt%　Ag2O/g-C3N4　as　a　good　photocatalyst　has　remarkable　photostability　under　visible　light　and　can　be　applied　to　alleviate　cyanobacteria　blooms.