The nitrite-reducing activity of aerobic denitrifying bacterial strain N6-1 was studied. It showed that the nitrite-reducing activity reached the highest at 30℃, 120 r/min, pH 8.5 and C/N ratio 12, using CH3COONa and NaNO2 as the sole carbon source and nitrogen source, respectively. When the initial NaNO2 concentration was 2 g/L, NO2--N was reduced completely after 20 hours cultivation with the reducing rate of 20.3 mg/L·h. There would be no effect on its nitrite-reducing activity in the present of 1.5% NaCl or 1% peptone. The cell concentration could reach 1.2×1011 CFU/mL after 24 hours cultivation in 10 L fermentor.