The equations of COD, nitrogen and phosphate mass balance is established and the results show that the COD, nitrogen and phosphorus balance ratios are 98.3%, 73.1%, 98.4%. COD removal is achieved by the discharge of aerobic oxidation and excess sludge, accounting for 86.3% of the total. The loss of nitrogen balance is due to the existing of SND. Nitrogen removal is mainly achieved by the discharge of denitrification process, including anoxic denitrification process (33.6%) and SND process (23.3%). In order to solve the problem of large energy consumption, some optimized control measures are proposed and the test results indicate that TN removal rate has increased from 89.2% to 93.1%, tons of water at power consumption has dropped from 0.35 to 0.26kW•h/m3.