A　granule-based　simultaneous　nitrification,　anammox,　and　denitrification　process　in　a　membrane　bioreactor　(SNAD-MBR)　was　performed　to　investigate　the　influence　of　in-situ　NaClO　backwashing　on　biological　performance　and　membrane　fouling.　First,　the　limit　of　the　NaClO　concentration　for　the　SNAD　granules　was　determined　(20　mg/g　center　dot　SS)　in　a　short-term　batch　test.　Then,　three　in-situ　NaClO　backwashing　strategies　(NaClO　concentrations　of　5-15　mg/g　center　dot　SS　with　backwashing　frequencies　of　1/10-1/30　min)　were　implemented　during　long-term　SNAD-MBR　process.　The　results　showed　that　the　removal　efficiencies　of　total　nitrogen　(TN)　and　chemical　oxygen　demand　decreased　from　92.69%　and　94.19%　to　81.82%　and　85.39%,　respectively,　with　an　increase　in　the　NaClO　concentration　in　spite　of　a　reduction　in　backwashing　frequency.　The　deterioration　of　the　biological　performance　could　be　explained　by　the　inhibitory　activities　of　the　functional　bacteria　after　long-term　exposure　to　NaClO.　Nevertheless,　the　stable　contributions　of　autotrophic　and　heterotrophic　processes　to　TN　removal　(Eanammox　of　91.23%,　Edenitrification　of　8.77%)　indicated　a　negligible　impact　of　NaClO　back　washing　on　the　balance　of　the　nitrogen　removal　pathways.　Furthermore,　membrane　fouling　was　significantly　suppressed　when　in-situ　NaClO　backwashing　was　performed　with　a　relatively　high　frequency　(1/1-10/20min)　and　a　low　concentration　(5-10　mg/g　center　dot　SS).　However,　a　higher　NaClO　concentration　(15　mg/g　center　dot　SS)　exacerbated　membrane　fouling,　although　the　backwashing　frequency　was　low.　Meanwhile,　the　high　fouling　potential　of　the　SNAD　granules　resulted　from　the　high　production　of　soluble　microbial　products　(especially　tryptophan　protein-like　substances)　under　NaClO　stress.　The　possible　underlying　mechanism　was　the　trade-off　between　the　membrane　scrubbing　effect　by　NaClO　and　the　variable　physico-chemical　properties　of　the　SNAD　granules.　The　optimal　in-situ　NaClO　backwashing　strategy　that　considered　the　process　performance,　membrane　fouling,　and　permeate　production　was　a　NaClO　concentration　of　15　mg/g　center　dot　SS　and　a　backwashing　frequency　of　1/20　min.　The　results　provide　guidance　for　in-situ　NaClO　backwashing　of　the　SNAD-MBR　process.