An　up-flow　micro-oxygen　membrane　bioreactor　(UMSB-MBR)　was　utilized　to　start　up　the　simultaneous　nitrification,　anaerobic　ammonia　oxidation　coupling　with　heterotrophic　denitrification　(SNAD)　process,　and　a　mathematical　model　was　planned　to　be　built　to　realize　the　start-up　process　analysis　and　the　optimization　process　prediction.　The　results　showed　that　the　SNAD　process　(the　total　nitrogen　removal　rate　of　87.66%)　started　up　successfully　by　inducing　the　carbon　source　(C/N　ratio　of　0.5)　after　anammox　and　completely　autotrophic　nitrogen　removal　(CANON)　processes　in　the　bioreactor,　and　the　start-up　model　of　the　SNAD　process　was　successfully　built　using　the　ASM1model　and　experimental　data;　the　model　analysis　revealed　that　the　increase　in　the　nitrogen　loading　rate　(NLR)　(from　0.24kg/(m3•d)　to　1.88kg/(m3•d))　and　the　suitable　dissolved　oxygen(DO)　(0.2~0.4mg/L)　accelerated　the　start-up　of　the　SNAD　process;　the　model　prediction　revealed　that　the　inhibition　of　anaerobic　ammonia-oxidizing　bacteria　(AnAOB)　from　denitrifying　bacteria　(DNB)　was　strengthened　with　the　increase　in　the　C/N　ratio　(from　0.5　to　3.0),　and　shifted　the　major　nitrogen　removal　pathway　from　anammox　to　heterotrophic　denitrification　process.　From　the　comprehensive　consideration,　the　appropriate　C/N　ratio　should　be　chosen　at　1.5under　which　the　process　performance　and　distribution　of　the　microbial　flora　could　be　at　the　best　state　of　the　SNAD　process.　©　2021,　Editorial　Board　of　China　Environmental　Science.　All　right　reserved.