In　this　study　the　effect　of　different　fouling　stages　of　hollow　fiber　membranes　on　effective　backwashing　length　in　MBR　has　been　investigated.　Computational　fluid　dynamics　(CFD)　is　imported　to　simulate　backwashing　process.　A　multi-physics　coupling　model　for　free　porous　media　flow,　convective　mass　transfer　and　diluted　species　transport　was　established.　The　laser　bijection　sensors　(LBS)　were　imported　to　monitor　the　backwashing　solution　position　inside　fiber　lumen.　Simulation　results　indicated　that　membrane　fouling　degree　could　change　the　velocity　of　backwash　solution　inside　fiber　lumen　and　make　a　further　effect　on　effective　backwash　length.　The　signal　variations　of　LBS　are　in　accordance　with　the　simulation　results.　The　backwashing　process　can　only　play　an　active　role　when　the　filtration　pressure　is　below　the　critical　TMP.　It　can　be　concluded　that　backwash　duration　in　industrial　applications　need　to　be　set　based　on　changes　in　TMP.