Polyaluminium chloride (PAC), also known as polyaluminum chloride, basic aluminum chloride, has the chemical formula ALn(OH)mCL3n-m. PAC is a multivalent electrolyte that significantly reduces the colloidal charge of clay-like impurities (multiple negatively charged) in water. Due to the large molecular mass and strong adsorption capacity, the formed flocs are larger, and the flocculation and sedimentation performance is superior to other flocculants. The PAC has a high degree of polymerization, and rapid stirring after the addition can greatly shorten the formation time of the flocs. The PAC is less affected by the water temperature, and the effect is also good when the water temperature is low. It has a lower pH value for water and a wide pH range (can be used in the range of pH=5 to 9), so it is possible to dispense an alkaline agent. The dosage of PAC is small, the amount of mud produced is small, and it is convenient to use, manage and operate, and it is less corrosive to equipment and pipelines. Therefore, PAC has a tendency to gradually replace aluminum sulfate in the field of water treatment.