HEDP?Na is an organophosphonic acid corrosion inhibitor, it can chelate with Fe, Cu, and Zn ions. HEDP?Na can dissolve the oxidized materials, it has good scale and corrosion inhibition effects even under 250℃, it is stable under high pH value, not easy to be hydrolyzed, not easy to be decomposed under normal light and heat condition, its acid/alkaline and chloride oxidation tolerance are better than that of other organophosph-onic acids. HEDP?Na can form six-ring chelating compounds with metal ions in water system, Ca2+ in particular. HEDP?Na has good scale inhibition effects and obvious dissolution threshold effects. When used with other Water Treatment Chemicals, the synergistic effects is better.