The Activated Sludge Models were widely applied in Europe and America since they were put forward, however, for an accurate simulation of the activated sludge treatment processes, reliable wastewater characteristic parameters such as COD components were needed. The conventional parameters such as COD can not differentiate the carbonaceous organic matters of wastewater, so they need to be divided again. Therefore, the fractionation of influent COD components in the Activated Sludge Models is introduced, and the physical-chemical and biological characteristics of each COD components are analyzed. The measurements of influent COD components are reviewed and some evaluation is made. The issue in determining the influent COD components is discussed. The idea of establishing a characterization guideline is put forward at last.