The　difficulties　in　enriching　anammox　bacteria　and　maintaining　stable　partial　nitrification　during　start-up　phase　limit　the　application　of　mainstream　anammox　process.　In　this　study,　the　feasibility　of　starting　up　simultaneous　partial　nitrification,　anammox　and　denitrification　(SNAD)　reactor　treating　municipal　wastewater　by　inoculating　ordinary　nitrification　sludge　(96.2%)　and　a　small　amount　of　anammox　sludge　(3.8%)　was　investigated.　A　sequencing　batch　reactor　with　intermittent　aeration　was　used　for　the　SNAD　process.　The　SNAD　reactor　was　started　up　in　75　days　with　a　nitrogen　removal　efficiency　of　85.4%　at　ambient　temperature.　The　nitrogen　removal　performance　maintained　stable　despite　the　fluctuating　inflow.　Anammox　bacterial　activity　exponentially　increased　although　nitrite　oxidizing　bacteria　(NOB)　activity　in　seeding　sludge　was　high.　The　enhanced　ammonium　oxidizing　bacterial　activity　and　partial　denitrification　provided　sufficient　nitrite　for　anammox　bacteria.　Moreover,　NOB　was　inhibited　by　intermittent　aeration,　anammox　bacteria　had　competitive　advantage　on　nitrite.　The　improved　particle　size　and　settleability　of　activated　sludge　also　favored　the　anammox　bacterial　enrichment.　This　study　provided　an　improved　and　easily-implemented　start-up　strategy　for　mainstream　anammox.　The　seeding　sludge　was　easily　obtained　and　the　operation　strategy　was　simple.　These　findings　were　meaningful　to　the　engineering　application　of　mainstream　anammox.