In order to ensure the stable and standard discharge of mixed nitrogen sewage, Guangzhou Datansha Wastewater Treatment Plant has made a test using an inverted A2/ O process, with the actual Wastewater as entry water. When the ratio of mixed fecal sewage is 0.33%, the results showed that, extending the HRT(Hydraulic Retention Time) can help to enhance the effect of removing nitrogen, and HRT should be ensured at least 8 hours under the test conditions. And the increase of the concentration of dissolved oxygen can promote the effect of removing nitrogen ranging from 1.0 to 1.5 mg/L. And the sludge reflux ratio should be remained at 60%. Besides, the growth of sludge age has positive effect on nitrification, so the sludge age should be controlled in more than 20 days under the experimental conditions.