Abstract: Surplus activated sludge was disposed of by a self-designed technology of one-stage preheated autothermal themophilic aerobic digestion. With the intermittent operating method，the influence of feed sludge concentration，agitation velocity，aeration and solid retention time (SRT) on sludge stability was investigated，and the effectiveness of sludge stability and harmlessness was evaluated，simultaneously，the dewatering function and pH were detected and analyzed. The results showed that when the total solid and VSS of feed sludge were 4.3%～6.4% and 33.4～44.1 g/L，agitation velocity was 100～110 r/min，aeration was 0.10～0.12 m3/h，SRT was 10 d，sludge digestion efficiency was the best，the temperature of inner tank was maintained at 54.5～56.8℃，the average removal rate of VSS reached 53.2%，the dehydrogenase activity (DHA) decreased by 74%，the inactivation rate of pathogens bacteria was 100%，the digested sludge met the class A biomass standard of US EPA. Under the best process conditions，sludge dewatering was worse，while pH increased，and this phenomenon was caused by cell lysis in the digestion process.