Abstract: The effects of simultaneous pretreatment with ultrasonic and thermo-chemical on high solid sludge disintegration for improved energy efficiency were investigated. The sludge was pretreated at specific energy of 9551 kJ·kg^-1 total solids (TS), temperature of 73℃, and alkaline dosage of 0.085 g·g^-1, which were optimal conditions obtaining maximum sludge disintegration in previous study. Experimental results show that the mean particle diameters (dp) of pretreated sludge with solid contents of 3%, 5%, 10%, and 15% were decreased by 40.14%, 58.01%, 93.63%, and 17.46%. Besides, the dp10, dp50, and dp90 of pretreated sludge with solid content of 10% decreased by 88.38%, 93.85%, and 96.74% after pretreatment. In terms of sludge disintegration, the increased soluble chemical oxygen demand (SCOD) concentration of pretreated sludge had a positive correlation with solid content of sludge, while the disintegration degree (DD) showed a reverse trend. The maximum DD of 50.3% was obtained in sludge with solid content of 3%. The organic matter composition of pretreated sludge was also examined. It indicated that soluble protein and carbohydrates concentrations of sludge with 10% solid content were much higher than those of sludge with 3%, 5%, and 15% solid content. Moreover, the biodegradability of pretreated sludge with 10% solid content was as high as 88.94%. Therefore, the simultaneous pretreatment with ultrasonic and thermo-chemical has a good application prospects in high solid sludge disintegration.