The paper reviews the research status of the secondary clarifier model from one-dimensional model to three-dimensional model. The one-dimensional model based on solid flux theory was outlined by discussing how to choose model parameters such as settling velocity function and the number of layers. Based on the achievement of actived sludge model and the development of wastewater treatment technology, it is suggested that the development of the secondary clarifier model should focus on the establishment of some clarifier model including biological processes and the enrichment of hydraulics phenomena modeling.