The　kinetics　of　polyamide　membrane　degradation　by　free　chlorine　and　halide　ions　(Br−　and　Cl−)　were　innovatively　evaluated　based　on　physicochemical　properties　and　filtration　performance,　using　water/solute　permeability　coefficient　in　addition　to　bromide　incorporation　as　important　indicators.　The　reaction　rate　constants　for　the　reduced　water　and　H3BO3　permeability　coefficient　were　1–2　orders　of　magnitude　higher　at　0–1　h　than　1–10　h.　N-bromination　and　bromination-promoted　hydrolysis　are　dominant　degradation　mechanisms　at　0−1　h　(reflected　by　the　breakage　of　hydrogen　bond,　the　increased　Ca　binding　content,　and　the　increased　charge　density),　and　ring-bromination　further　occurs　at　1−10　h　(reflected　by　the　disappearance　or　weakening　of　aromatic　amide　band　and　the　nearly　constant　hydrogen　bond).　The　more　reactive　but　less　abundant　brominating　agents　(Br2O,　BrOCl,　BrCl,　and　Br2)　played　significant　roles　in　membrane　degradation,　contradicting　the　conventional　belief　that　HOBr　is　the　only　reactive　species.　BrCl　at　pH　4.0　and　BrOCl　and　Br2O　at　pH　7.0　made　significantly　higher　contributions　to　membrane　degradation　than　HOBr　(＞76　%　vs.　2　with　the　increased　[Cl−]　and　[Br−]ex　(the　excess　bromide,　defined　as　[Br−]o　−　[HOCl]o　when　[Br−]o　＞　[HOCl]o),　respectively,　was　responsible　for　the　greater　reduction　of　water　permeability　coefficient.　The　innovative　and　simple　approach　developed　in　this　study　provides　important　insights　to　evaluate　and　predict　membrane　degradation.　©　2024