Activated sludge model is playing a more and more important role in the design, operation, and administration of the wastewater treatment plants. Since 1950s the study on model have achieved great advance. The development of activated sludge model is reviewed and discussed from the mechanism, function and description. The advantage and disadvantage of several important models, including Eckenfelder model,McKinney model,Lawrence_McCarty model,Andrews model,WRc model and IWA model, are compared. On the basis of the achievement of the modern environmental microbiology and the development of wastewater analysis technology, it can be concluded that the development of the activated sludge model may focus on more detailed characterization of wastewater and the establishment of the system of automatic control and design.