NOVELTY - Culture technique of nitrifying bacteria for treating sewage, involves (a) transferring mixture of sludge water and returned sludge to-be-treated into an aerobic tank, and oxidizing ammonia and nitrogen in the sludge water using nitrifying bacteria in the returned sludge, (b) transferring the obtained solution into an anaerobic tank, (c) transferring the obtained solution from anaerobic tank into precipitation tank for separating the sludge and water, and (d) collecting residual precipitated sludge as activated sludge for culturing the nitrifying bacteria.    USE - The culture technique of nitrifying bacteria are useful for treating municipal sewage, where the nitrifying bacteria is Nitrosomonas or Nitrospira (claimed).    ADVANTAGE - The nitrifying bacteria enhances the removal of biological nitrogen and phosphorus from the sewage.    DETAILED DESCRIPTION - Culture technique of nitrifying bacteria for treating municipal sewage, involves (a) transferring mixture of sludge water and returned sludge to-be-treated into an aerobic tank comprises an aerating device, oxidizing ammonia and nitrogen in the sludge water to-be-treated into nitrate using nitrifying bacteria in the returned sludge under aerobic condition, where the sludge concentration in the aerobic tank is 2-4 g/l, hydraulic retention time is 24-36 hours and concentration of dissolved oxygen is 2-3 mg/l, (b) transferring the obtained nitrified mixed solution into anaerobic tank comprising an agitating device, where the denitrifying bacteria induces the reaction of organic substances in the sludge waste with the nitrate produced through the nitrification in the aerobic tank so as to reduce the nitrate into nitrogen under anaerobic condition, the sludge concentration in the anaerobic tank is 2-4 g/l, the hydraulic retention time is 6-9 hours and oxidation-reduction potential is -100 to 0 mV, (c) transferring the obtained solution from anaerobic tank into precipitation tank for separating the sludge and water by directly discharging supernatant together with outlet water of sewage treatment plant, or treating the supernatant to inlet of the sewage treatment plant for further treatment and adding obtained precipitated sludge to the aerobic tank to form the sludge reflux with reflux ratio of 30-50%, and (d) collecting residual precipitated sludge as activated sludge for culturing the nitrifying bacteria, where the concentration of nitrifying bacteria is 20-30%.