A heterotrophic nitrification and aerobic denitrification strain L3 was separated and identified from bioflocs in the aquacultural system, to investigate the influential factors of bacterial growth and the denitrification performance. The result of 16S rRNA gene sequence analysis showed that the strain L3 was Pseudomonas. The optimum pH for the growth of strain L3 was 6 to 8, the suitable carbon source was sodium succinate, and the optimum temperature was 25-35℃, with the optimum C/N from 10 to 15. The strain L3 could tolerate the high ammonia concentration. By studying the characteristics of heterotrophic nitrification and aerobic denitrification, the strain L3 was found to preferentially remove ammonia and had good aerobic denitrification performance.