The　rapid　start-up　of　Partial　denitrification　(PD;　nitrate　to　nitrite)　was　investigated　based　on　the　analysis　of　microbially　driven　mechanism　of　nitrite　accumulation　mediated　by　Dissolved　organic　matter　(DOM)　in　this　study.　The　nitrate　to　Nitrite　transformation　ratio　(NTR)　＞　90%　and　effluent　nitrate　＜　5　mg/L　were　achieved　in　17　days　by　feeding　with　lower　nitrate　of　similar　to　35　mg/L　and　removing　the　idling　period.　And　the　enhanced　nitrite　accumulation　when　applying　the　above　strategy　is　related　to　the　decreased　utilization　of　the　aliphatic　DOM　during　nitrite　reduction　process.　Additionally,　the　rapid　enriched　Thauera　and　OLB13　(37.21%)　and　inhibited　norank_f_Blastocatellaceae　(2.86%),　and　the　increased　disparity　(2.0-fold)　between　the　genes　involved　in　nitrite　generation　(e.g.,　narH)　and　for　nitrite　reduction　(e.g.,　nirK)　jointly　contributed　to　PD　start-up.　While　the　genes　(e.　g.,　DLD)　related　to　producing　electrons　from　aliphatic　DOM　also　up-regulated　by　0.1-fold,　which　led　to　the　increased　nitrate　removal　and　NTR.