To evaluate the influence of thermal hydrolysis pretreatment (THP) following anaerobic digestion (AD) of high solid content sludge, the transformation characteristics of carbon, nitrogen, phosphorus and sulfur during the THP-AD process of dewatering sludge from municipal wastewater treatment plant (WWTP) was investigated using THP reactor (165 ℃,50 min) and four lab-scale completely mixed anaerobic digesters (mesophilic and thermophilic, HRT=20d).The experimental results indicated that over 40% of VSS was hydrolyzed after THP, and dissolved protein and carbohydrate were the main component of dissolved organic matter in hydrolysate.