Abstract: Thermal corrosion behavior of 12Cr1MoVG steel for heat pipe in waste incinerator in mixed molten salts were studied by corrosion kinetic method, corrosion surface observation and micro area composition analysis; the mixed molten salts were KCl+NaCl, KCl+K₂SO₄, NaCl+Na₂SO₄ and K₂SO₄+Na₂SO₄, respectively, whose molar ratios were all 1:1. The results show that the corrosion mass change and corrosion depth of the tested steel in molten salt of KCl+NaCl were higher than those in molten salt of K₂SO₄+Na₂SO₄, holes of different size were produced in the corrosion layer and chlorine already penetrated into the substrate. The corrosion effect of alkali metal chloride salt on the tested steel was greater than that of alkali metal sulfate salt. The corrosion mass change and corrosion depth of the tested steel in KCl+K₂SO₄ molten salt were greater than those in NaCl+Na₂SO₄ molten salt and the corrosion layer was looser. The corrosion ability of the potassium salt to the tested steel was stronger than that of the sodium salt. The corrosion rate of the tested steel from large to small was listed as follows:KCl+NaCl, K₂SO₄+Na₂SO₄, KCl+K₂SO₄, NaCl+NaSO₄.