Poly aluminum chloride (PAC) is an inorganic substance, an emerging water purification material, inorganic polymer agent, simply polyaluminum. It is a water-soluble inorganic polymer polymer between AlCI3 and Al(OH)3 with the chemical general formula [Al2 (OH) n Cl 6-n] m where m represents polymerization and n represents the neutrality of the PAC product. n=1~5 is a high-charged polymeric ring chain with Keggin structure, highly electroneutral on colloids and particulate matter in water, and can strongly remove microtoxic and heavy metal ions, with stable characteristics.