In order to understand the corrosion of the austenitic stainless steel in the molten salt of the ternary mag- nesium-based chloride NaCl-CaCl₂ -MgCl₂ during a thermal storage,the corrosion behaviors of five kinds of stainless steels (201,304,310S,316L and 321) after being corroded in the molten salt in a short term were investigated by means of the mass loss measurement.Then,a long-term corrosion test on 316L stainless steel which had shown a better corrosion resistance in the short-term corrosion test was conducted.Finally,the changes of the corrosion phase and morphology with the corrosion time were analyzed by means of XRD and SEM.The results show that (1) when the five kinds of stainless steels are immersed in an open crucible full of the molten salt,they suffer more ob- vious corrosion mass loss than those with a capped crucible do; (2) 316L stainless steel which contains Mo shows a better corrosion resistance at any one of 500,600 and 700 ℃,furthermore,the annual corrosion rate of 316L stainless steel at 600℃ is 0. 347mm per year; (3) the diffraction peak of 316L stainless steel substrate still ap- pears in the pattern after a five-day corrosion,but after a ten-day immersion,the diffraction peak of MgO appears; and (4) the surface of 316L stainless steel is porous after a five-day corrosion,and then,after a ten-day immer- sion,the corrosion pores are gradually filled by MgO,which is formed by means of the hydrolysis of MgCl₂2 at high temperatures.