Anaerobic digestion is an economically viable and environmentally friendly process for the reduction of excess municipals sludge. Primary and activated sludge are generated during wastewater treatment. This article adopted semi-continuous flow experiments of an aerobic digestion in the middle temperature for excess sludge from the wastewater treatment plant of Jinzhou Petrochemical Plant of China Petroleum. Fluctuation conditions of pH, volatile fatty acid (VFA), chemical oxygen demand (COD), volatile solid sludge (VSS), and gas production are all tested, respectively. The result shows that: pH increased from 6.3-7.2, which agrees with the reported pH changes in full-scale facilities. The removal ratio of COD and VSS are 70.3% and 55.6%, respectively, which implies that the process is an effective treatment Maximum gas production is 864 ml (CH4 content is 60.3%). The VFA had shown a sharp decline under the low ratio of sludge dosage conditions. The concentration variation of VFA was gradually stabilizing with advanced he ratio of sludge dosage. Anaerobic digestion performance of municipal sludge was very good; however, further research should take into account a balance between performance enhancement and economic cost.