Polyaluminium Chloride Reacts with Conventional Coagulants As a new type of water treatment agent, PAC has replaced traditional aluminum sulphate since the 1960s but its flocculation effect is significantly higher than that of aluminum sulphate The root cause has not been clearly stated, and there has been controversy, which to a certain extent affected its production and application to a higher stage of development. A corollary is that the traditional pharmaceuticals are put into direct contact with water and their hydrolytic formation state can not form the most effective flocculation form and exert their highest efficiency due to the constraints of water quality and the like, while the production of PAC is prefabricated under artificially controlled conditions , Can achieve the expected best results, into the water can play the role of electricity and bridging the excellent flocculation effect, although this idea is reasonable, but not necessarily perfect, and not been experimentally proven, there is a great Research space. In the long-term research work, we found that artificially prefabricated aluminum or iron polymers, from morphology, characteristics, function to mechanism of action, are greatly different from the previous aluminum salt or iron salt coagulant and should be considered as A new generation of products, you need to establish their own theoretical and technological process system, the paper selected a number of experimental examples of PAC to illustrate this issue. The traditional methods of aluminum complexing are chemical analysis and potentiometric titration. Proposed a series of continuous changes in the hydrolysis of the series, the hydroxy compound state by the monomer polymer, according to the six-ring model until the formation of precipitation still maintain the structure of Bayerite, the theoretical basis of this view is the polynuclear complex Nuclear chain complexation mechanism, dominated for decades, but there is no direct proof of structure identification.