Abstract: The pollution of ammonia nitrogen has seriously affected the healthy aquaculture of shrimp. In order to screen the microecological bacteria suitable for the efficient degradation of ammonia nitrogen in shrimp aquaculture, four strains including FS007, FS008, FS017 and FS025 with the strong effect of ammonia nitrogen degradation were obtained from 25 strains isolated from the early stage of the laboratory through the detection of ammonia nitrogen degradation. Among them, FS017 was the best strain with the degradation of ammonia nitrogen. After 24 h of culture, its morphological identification was carried out:The bacterial colony was white, the surface was wetting, the edge was smooth and round, and there was mucilage in the middle, while the cells were positive for gram staining, rod-shaped and arranged in short chain or Beadlike chain together with elliptic and central endospores. And the physiological and biochemical tests were also carried out:the results of casein, glucose, gelatin, xylose, mannitol, arabinose, starch, citric acid, nitrate reduction, methyl red test, catalase, VP reaction, aerobism and NaCl(2%-12%) were all positive, while the results of aerogenesis, fructose and propionate H₂S were negative. Therefore, the bacterium was identified as Bacillus velezensis by 16S rDNA molecular identification.