Abstract: Extracellular polymeric substances (EPS) is a common microbial by-product of biological treatment process in wastewater treatment plants. Its occurrence has different effects on various processes of wastewater treatment system. Firstly, on the basis of previous studies, the definition of EPS was summarized, and the structure, compositions and functions of it was described in detail. Secondly, the effects of EPS on the growth of microorganisms, the formation of granular sludge, the flocculation and sedimentation performance of microbial aggregates in the biological treatment process, the permeability of the membrane and the mass transfer of the catalyst in the advanced treatment process, the impact of sludge digestion and dehydration performance in the sludge treatment process were reviewed. The behavior mechanisms of EPS in different wastewater treatment process were summarized and explored. Finally, the future research directions and contents of EPS in wastewater treatment were proposed.