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With the widely use of biological wastewater treatment, a large number of sewage sludge (SS) was produced in the process. The treatment of SS has become a major challenge for wastewater treatment plants. Landfill and incineration as traditional methods of sludge treatment not only pollute the environment but also consume a lot of energy. Anaerobic digestion as a sustainable sludge treatment method benefits environmental protection and energy saving. However, traditional anaerobic digestion of sludge treatment has the characters of low efficiency, poor biodegradability and long residence time. Therefore, in order to improve the efficiency of anaerobic digestion of SS, the pretreatments are paid more and more attention. According to the physical and chemical properties and the anaerobic digestion of sludge characteristics, this study assessments the different mechanisms of various sludge pretreatment methods. Simultaneously, different types of sludge pretreatment were classified. And the effects of different types of sludge pretreatment on the characteristics of anaerobic digestion of sludge were compared further. Moreover, the influence factors of different sludge anaerobic digestion treatment were evaluated deeply. Besides, the problems of anaerobic sludge digestion and the direction for the future development of anaerobic sludge digestion were briefly analyzed.