Abstract: Extracellular polymeric substances( EPS) is an important determinant of the characters of sludge produced in biological wastewater treatment processes,including the structure,dewaterability,flocculation and settling behavior. However,the different extraction methods of EPS leaded to more discrepancy of EPS stripping degree. Thus,the establishment of the EPS extraction from sludge method is crucial. Six different methods were employed to extract EPS from different sludge in this study,and the content and composition of EPS in different sludge layers were analyzed. Meanwhile,the relationship between the sludge particle size and dewatering performance and the EPS were investigated.Resultsshow that the EPS content is different in different processes of reactor. Formaldehyde + Na OH extraction method was proved to be the most efficient method to extract EPS from sludge,and the destructiveness on cells of this method was relatively slight. The extracted EPS content of different sludge of the method is in the range of 15. 88- 39. 30 mg / g VSS. The content of slime-EPS is higher,the ratio of protein and polysaccharide is larger,but the dewaterability of the sludge is poorer. Besides,the sludge particle size is greater,and the extraction efficiency of EPS is higher.