In this paper, a new and highly efficient denitrifying bacterium strain from Poyang Lake was screened and named X10. The physiological and biochemical characteristics, 16S rDNA gene sequence analysis, and the effects of nitrite concentration, pH value, temperature and inoculum size on the growth and nitrogen removal ability of the strain were researched. Meanwhile, the nitrite degradation capacity of X10 in aquaculture water was also studied. The results showed that the strain X10 was identified as Acinetobacter xylosoxidans. The optimal incubation conditions for the aerobic denitrifying strain X10 were: pH, 7.0; inoculation size, 3%; temperature, 30 ℃; nitrite concentration, 300 mg/L. Under this circumstance, the degradum rate of nitrite reached peak after 48 h, up to 99.8%. When X10 bacteria (2×10⁸ CFU/mL) were added into cultured pond water (28℃), the degradation rate of nitrite was 82.6% after 96 h. The safety evaluation test showed that the high concentration of X10 (5 × 10⁸ CFU/mL) had no lethal effect on Danio rerio and no hemolysis was found. These results indicated that X10 can be applied widely in aquaculture.