The invention relates to the field of sewage treatment, and specifically discloses an aerobic denitrification bacterial agent, including Klebsiella pneumoniae bacterial liquid, Raoultella vegetative bacterial liquid, Bacillus flexus bacterial liquid, Sphingobacterium bacterial liquid, Gram Lebsiella bacteria liquid, Acinetobacter baumannii bacteria liquid and Pseudomonas steerii bacteria liquid. A method for preparing an aerobic denitrifying bacterial agent, comprising the following steps: step a: activation of strains; step b: expanded cultivation; step c: preparing the bacterial agent, mixing the bacterial liquid in step b to prepare a mixed bacterial liquid, Inoculate the mixed bacterial solution into the aerobic denitrification medium and culture it with constant temperature shaking for 24h~48h. When the total number of microorganisms is greater than 10 9 When the CFU / ml is used, the bacterial agent is collected and divided into sterile containers for storage. The technical solution solves the problems of high cost and difficult management in the sewage treatment process in the prior art.