Abstract: In this study,the wet sludge obtained from a municipal sewage treatment plant was pretreated with sodium dodecyl sulfate（SDS）and subcritical water. Hydrothermal liquefaction of pretreated sludge was carried out under the conditions of reaction temperature of 340 °C and residence time of 40 min. The effects of pretreatment conditions on sludge organic matter extraction,liquefaction products yield and bio-oil composition were studied. Results showed that after pretreatment the content of organic matter extracted from sludge was significantly improved. The highest bio-oil yield and ester content were 43.70% and 58.67%,respectively.