Abstract：Nitrate reduction to nitrite for nitrite accumulation through controlling the reaction time in denitrification was investigated in a sequencing batch reactor (SBR) with sodium acetate as the electron donor under different C/N (COD/NO3--N) ratios. When the reaction time was reduced from 60 to 20 minutes nitrate reduction rate and nitrite accumulation rate respectively increased to 0.417 g·g-1·h-1 and 0.402 g·g-1·h-1. Nitrite accumulation rate could reach more than 95% after 108 days of cultivation. The denitrifier activity increases with the increase of C/N ratios. Low C/N ratios favor nitrite accumulation. When carbon source was sufficient, electron acceptor (nitrate and nitrite) competition and nitrate inhibition resulted in nitrite accumulation. However, nitrite accumulation occurred due to lack of substrate under carbon limitation. Results of Metagenomic sequencing analysis demonstrate that Thauera dominated in the microbial community of the culture, accounting for 71.85% of total population. This bacterium may play a major role in nitrate reduction to nitrite.