How　to　precisely　describe　the　fouling　behavior　of　activated　sludge　suspension　in　constant　flux　cross-flow　filtration　is　a　challenge.　In　this　paper,　a　three-mechanism　(standard　pore　blocking,　complete　pore　blocking　and　cake　filtration)　model　was　established　based　on　the　classic　blocking　law　to　describe　the　fouling　behavior　of　activated　sludge　suspension　in　the　constant　flux　cross-flow　filtration.　The　results　showed　that　the　predictions　of　the　proposed　model　showed　good　agreements　with　experimental　data　not　only　for　activated　sludge　suspension　(R-2　＞=　0.994),　but　also　for　bovine　serum　albumin　protein　(BSA)　(R-2　＞=　0.966),　humic　acid　(HA)　(R-2　＞=　0.940),　sodium　alginate　(SA)　(R-2　＞=　0.801)　and　kaolin　(R-2　＞=　0.961).　Meanwhile,　for　activated　sludge　suspension,　the　variation　rate　of　the　cake　resistance　increased　with　the　filtration　flux,　and　the　steady　available　membrane　area　ratio　(A(steady)/A(0))　was　independent　on　the　filtration　flux　while　it　decreased　with　the　increase　of　MLSS　concentration.　In　addition,　the　available　membrane　area　ratio　(A(t)/A(0))　decreased　slower　for　activated　sludge　suspension　than　that　for　single　model　solution　(BSA,　HA　and　SA)　in　the　fouling　process.