The hot corrosion behavior of the austenitic heat-resistant steel weld metal produced by multi-pass gas tungsten arc welding was investigated. A bilayer oxide scale formed on the surface of the weld metal by the selective oxidation of the element Cr and Fe, and the dissolution of the oxide film occurred at elevated temperatures due to the existence of the molten salt. Morphologies and structures of the oxide scale were characterized by electron microscopy and X-ray diffraction techniques, and then the underlying reason for the hot corrosion of the nonequilibrium weld metal was identified. The interdendritic region could act as the shortcut path for the oxygen, which promotes the internal oxide distribution in chains, and a large internal oxidation zone appears under the bilayer oxide scale.