A　novel　plasmonic　Ag/AgCl@LaFeO3　(ALFO)　photocatalyst　was　successfully　synthesized　by　a　simple　in-situ　synthesis　method　with　enhanced　photocatalytic　activity　under　visible　light　for　harmful　algal　blooms　(HABs)　control.　The　structure,　morphology,　chemical　states,　optical　and　electrochemical　properties　of　the　photocatalyst　were　systematically　investigated　using　a　series　of　characterization　methods.　Compared　with　pure　LaFeO3　and　Ag/AgCl,　ALFO-20%　owned　a　higher　light　absorption　capacity　and　lower　electron-hole　recombined　rate.　Therefore,　ALFO-20%　had　higher　photocatalytic　activity　with　a　near　100%　removal　rate　of　chlorophyll　a　within　150　min,　whose　kinetic　constant　was　15.36　and　9.61　times　faster　than　those　of　LaFeO3　and　Ag/AgCl.　In　addition,　the　changes　of　zeta　potential,　cell　membrane　permeability,　cell　morphology,　organic　matter,　total　soluble　protein,　photosynthetic　system　and　antioxidant　enzyme　system　in　Microcystis　aeruginosa　(M.　aeruginosa)　were　studied　to　explore　the　mechanism　of　M.　aeruginosa　photocatalytic　inactivation.　The　results　showed　that　ALFO-20%　could　change　the　permeability　and　morphology　of　the　algae　cell　membrane,　as　well　as　destroy　the　photosynthesis　system　and　antioxidant　system　of　M.　aeruginosa.　What＇s　more,　ALFO　could　further　degrade　the　organic　matters　flowed　out　after　algae　rupture　and　die,　reducing　the　secondary　pollution　and　avoiding　the　recurrence　of　HABs.　Finally,　the　species　of　reactive　oxygen　species　(ROS)　(mainly　center　dot　O-2(-)　and　center　dot　OH)　produced　by　ALFO　were　determined　through　quenching　experiments,　and　a　possible　photocatalytic　mechanism　was　proposed.　Overall,　ALFO　can　efficiently　remove　the　harmful　algae　under　the　visible　light,　providing　a　promising　method　for　controlling　HABs.