Isolation and identification of an efficient aerobic denitrifying bacteria strain by using the selective medium to isolate and screen aerobic denitrifying bacteria through the quantitative increase of nitrite content, after a preliminary screening, and then second screening through denitrification performance testing for bacterial isolation. Physiological and biochemical tests and 16S rRNA gene amplification and blasting in GenBank ,and phylogenetic tree construction were used to identify the selected strain. Only the DB-6 with effective denitrification .During 5 days, NO₂^- -N was decreased from 3 570 mg/L to 22 mg/L, the removal efficiency was 99.4%, NO₃^- -N was decreased from 2 464 mg/L to 27 mg/L, the removal efficiency was 98.9% and without nitrite accumulation. The strain was identified as Enterobacter cloacae DB-6 according to its morphological, physiological and biochemical characters. In order to further confirm the result, 1 445 bp sequence of DB-6 16S rRNA was amplified and blasted in GenBank. Homology analysis study showed that DB-6 has the highest similarity to Enterobacter cloacae with 99% identity. And phylogenetic tree was constructed together with the discovered nitrifying bacteria, denitrifying bacteria and Enterobacter cloacae. It was suggested that Enterobacter cloacae DB-6 be a novel strain of aerobic denitrifying bacteria,which will be helpful in nitrogen removal of mariculture water.