HEDP•Na2 is an organophosphonic acid corrosion inhibitor, it can chelate with Fe, Cu, and Zn ions, it 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•Na2 can form six-ring chelating compounds with metal ions in water system, Ca2+ in particular. HEDP•Na2 has good scale inhibition effects and obvious dissolution threshold effects. When used with other Water Treatment Chemicals, the synergistic effects is better.