Gravity-driven　membrane　(GDM)　ultrafiltration　is　a　promising　water　treatment　method　due　to　its　low　energy　consumption　and　low　maintenance.　However,　the　low　stable　permeability　in　algae-laden　water　treatment　is　currently　limiting　its　wider　application.　With　the　ultimate　goal　of　increasing　permeability,　the　aim　of　this　study　was　to　evaluate　the　effect　of　a　composite　coagulant　of　aluminum　sulfate-chitosan　(AS-CS)　on　the　GDM　filtration　performance.　In　parallel　tests　with　a　single　AS　coagulant　and　without　pre-coagulation,　the　analysis　of　membrane　fouling　resistance　and　the　membrane　fouling　mechanism　were　evaluated.　The　results　indicated　that　the　AS-CS/GDM　system　can　alleviate　23.74%　and　58.80%　membrane　fouling,　respectively,　compared　with　AS/GDM　and　the　GDM　system.　The　AS-CS/GDM　system　can　effectively　remove　humic-like　substances　having　a　molecular　weight　(MW)　of　3-100　kDa,　resulting　in　removal　of　98.32%　of　algae　cells　and　removal　of　66.25%　of　dissolved　organic　carbon;　the　AS-CS/GDM　system　thereby　improved　the　concentration　of　attached　biomass　on　the　membrane　surface　with　the　stronger　biodegradability　of　organic　matters.　The　application　of　AS-CS　pre-coagulation　in　the　GDM　process　could　enhance　the　proliferation　of　microorganisms　and　the　removal　of　low　molecular　weight　humic-like　substances.　Therefore,　the　AS-CS/GDM　system　is　a　potentially　important　approach　for　algae-laden　water　treatment.