Abstract: Comprehending the past results on the species distribution of polyaluminum chloride, a Double and Continous Hydrolysis model of species distribution and transformation of polyaluminum chloride is presented on the basis of the Double Hydrolysis model, and the species distributions and transformations of four series of Polyaluminum Chloride are explained. It is considered that the polymer and polynuclear species can be transformed each other, and the same transformation can appear between polynuclear species, provided that the conditions are changed.