To　investigate　the　effect　of　pH　on　the　production　of　N2O　during　shortcut　denitrification　process,　NaNO2　was　added　into　the　system　to　ensure　that　the　initial　concentration　of　NO2--N　was　40mg/L.　HCl　and　NaOH　were　used　to　regulate　pH　of　the　system　using　sequencing　batch　reactor　with　volume　of　2.4L.Results　showed　that　nitrite　reduction　rate　under　different　pH　varied　little　in　the　shortcut　denitrification　system.　The　maximum　nitrite　reduction　rate　was　0.084mgN/(mgMLSS·h)　and　the　minimum　nitrite　reduction　rate　was　0.071mgN/(mgMLSS·h);the　production　of　N　2O　could　reach　4.272mgN/L,which　accounted　for　10.68%　of　influent　nitrite　concentration　during　nitrite　denitrification　when　pH　was　6.5.　The　production　of　N2O　reached　only　0.573mgN/L　when　pH　was　8.0.　The　reasons　of　high　production　of　N2O　under　low　pH　during　denitification　process　were　mainly:(1)　low　pH　had　strong　inhibition　on　N2O　reductas;　(2)low　pH　played　a　role　of　screening　strains.　©　2011　IEEE.