Poor　resistance　to　free　chlorine　severely　impairs　the　service　of　conventional　polyamide　(PA)　membrane　in　water　treatment.　Here　we　design　a　series　of　superhydrophilic　aromatic　sulfonate　materials　(ASMs)　comprising　successively　increasing　conjugated　systems　and　ionizable　groups　(ASM-1,　ASM-2,　ASM-3)　to　develop　a　chlorine-resistant　membrane　via　chemical　modification.　By　altering　the　membrane　physicochemical　properties　and　surface　structure,　ASMs　substantially　improve　the　chlorine　resistance　and　water　permeability　of　membrane.　With　0.5　M　NaCl　as　the　draw　solution,　all　ASMs　enhance　membrane　water　fluxes　by　more　than　60%　relative　to　those　of　the　nascent　PA　membrane　in　forward　osmosis　(FO)　processes.　After　exposed　to　a　1000　ppm　sodium　hypochlorite　solution　for　2-8　h,　the　modified　membranes　exhibit　smaller　variations　in　FO　performance　than　the　PA　membrane.　Having　the　largest　conjugated　system　and　the　most　sulfonate　groups,　ASM-3　enables　the　membrane　to　sustain　a　chlorination　strength　of　up　to　8000　ppm·h　with　an　insignificant　NaCl　loss　during　the　FO　process,　surpassing　other　recently　developed　PA　membranes　in　chlorine　resistance.　These　results　manifest　that　the　combination　of　a　large　conjugated　system　and　ionizable　group　is　key　for　imbuing　membrane　with　excellent　chlorine　resistance　and　water　permeability.　Copyright　©　2020　American　Chemical　Society.