Characteristics　of　nitrite　accumulation　during　denitrification　process　were　studied　by　using　methanol　as　the　sole　organic　carbon　in　a　batch-scale　sequencing　batch　reactor　with　synthetic　wastewater.　Under　the　condition　of　temperature　was　14°C,　initial　pH　value　was　7.33　and　sludge　concentration　was　1000　mg·L-1,　nitrite　accumulated　significantly　during　denitrification　process.　Nitrite　concentration　increased　gradually　with　nitrate　reduction　and　reached　its　maximum　value　of　22.35　mg·L-1　in　2.5　h　when　nitrate　reduction　was　almost　completed,　the　amount　of　accumulated　nitrite　was　equivalent　to　43.2%　of　the　amount　of　initial　nitrate.　During　this　period,　pH　value　gradually　increased　to　7.79　in　2.67　h.　Then　accumulated　nitrite　kept　decreasing　until　to　zero.　When　the　concentration　of　nitrate　reduced　to　zero,　the　increasing　rate　of　pH　rise　dramatically,　formed　a　breakpoint　of　pH　curve.　Therefore,　the　breakpoint　of　pH　curve　can　be　used　as　an　indicator　to　show　the　end　of　nitrate　reductive　reaction.　The　pH　value　reached　its　maximum　value　of　8.35　in　3.5　h　and　decreased　a　little　afterward.　The　reason　for　the　accumulation　of　nitrite　is　the　inhibition　of　nitrate　on　nitrite　reductive　reaction,　caused　the　reductive　rate　of　nitrate　was　more　than　that　of　nitrite.