Operating temperature waves nearly melt temperature of molten eutectic NaCl-MgCl₂ which is thermal storage media at medium-high temperature. But corrosion behavior of the molten salt on metal at different temperature is not clear. Corrosion behavior and mechanism of the molten salt on Fe-14Cr-Mn alloy were studied by immersion salt corrosion method at 718K, 768K and 818K. Results show that corrosion rate increased lightly with the corrosion temperature. Corrosion kinetics characteristics obey linear law (slop is about k=-4.806E-4). At the early stage of corrosion, there was lots of vacuoles-shape, while a large number of pot hole formed after corroding 80h. Corrosion products are mainly Fe, Fe-Cr and MgO. Corrosion mechanism as follows: Absorbed oxygen on molten salt surface and oxygen atom that introduced in the form of moisture-absorbed MgCl₂ is depolarizing agents. Chloride of Cr and Mn is got when oxide of Cr and Mn react with Cl_-. The chloride of Cr and Mn with water (for example CrCl₃.6 (H₂O) and MnCl₂.n (H₂O)) that has low melting point will escape from corrosion system. In addition, there is a salt crust that is composed of MgCl₂. (H₂O) ₆, NaCl and MgO on molten salt upper surface, while NaCl coexists with NaMgCl₃ inside mixture salt. The study laid the foundation for the study of corrosion-resistant alloy in molten NaCl-MgCl₂.