Hydroxyethylidene diphosphonic acid (HEDP) is a new type of chlorine-free electroplating complexing agent. It is used as the main agent for water quality stabilization in the circulating cooling water system and plays a role in corrosion and scale inhibition. This product is one of the organic polyphosphonic acid water treatment agents. There are some other varieties of this type of products produced in China, such as aminotrimethylenephosphonic acid (ATMP): [CH2PO(OH)2]3N and ethylenediaminetetramethylenephosphonic acid (EDTMP), etc. Organic polyphosphonic acid is a type of water treatment agent developed in the late 1960s and confirmed around the 1970s. The emergence of this type of treatment agent has made a big step forward in water treatment technology. Compared with organic polyphosphates, organic polyphosphonic acid has the characteristics of good chemical stability, not easy to hydrolyze, high temperature resistance, small dosage, and corrosion mitigation performance. It is a type of cathodic corrosion inhibitor and a type of non-chemical equivalent scale inhibitor; when used in combination with other water treatment agents, it shows an ideal synergistic effect. It has excellent chelating ability for many metal ions such as calcium, magnesium, copper, zinc, etc., and even has a good deactivation effect on inorganic salts of these metals such as CaSO4, CaCO3, MgSiO3, etc., so it is widely used in water treatment technology.