A nickel based single crystal high-temperature alloy was subjected to two different heat- treatments, namely complete heat treatment (CH) and long-term aging after complete heat treatment (CH-LA).Then their hot corrosion behavior beneath a 75%Na₂SO₄ + 25%NaCl mixed salt film in air at 900℃ was studied by means of metallographic microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) methods, in terms of the surface morphology, phase composition, and element distribution of the alloy after 100 h corrosion. The results indicate that fine γ-particles with good cubic degree are uniformly distributed on the matrix γ' phase for the CH alloy. While the γ'-phase was deformed coarsened, and rafted, meanwhile spherical, needle like, and short rod like TCP phases did precipitated for the CH-LA alloy. The corrosion kinetics curves of the two different heat-treated alloys are similar to parabolas or segmented parabolas. The corrosion rate of CH alloy is relatively small, while a continuous Al₂O₃ outer oxide scale is formed on the surface, and Al internal oxidation and Cr, Ni internal sulfidation occur in the inner layer, and slight spallation of the corrosion product scale was observed. The CH-LA alloy shows a relatively high corrosion rate with significant spallation of the formed surface corrosion products, which is a thick composite oxide scale with an extremely thin Al₂O₃ scale on the surface, beneath that, there is a zone of internal oxidation of Al and internal sulfidation of Cr and Ni.