The work aims to study corrosion behavior and mechanism of four heat-resistant alloys for AUSC power plant boilers including Haynes 625, Haynes 617, Haynes 120 and Inconel 740H in a simulated coal-ash environment at 750 ℃. The corrosion products on samples were characterized by means of XRD, SEM and EDS. Four superalloys exhibited certain resistance to high temperature simulated coal-ash corrosion. Corrosion kinetics of experimental materials without coal-ash followed a parabolic corrosion law, which indicated that high temperature corrosion behavior of the selected alloys at 750℃ was controlled by ion diffusion. Weight gain of materials in simulated coal-ash environment was as follows: Haynes 617 > Haynes 625 > Inconel 740H > Haynes 120. Corrosion products on the surface of Haynes 625 and Haynes 617 were oxides of bilayer structures. Internal oxidation layer was Cr-enriched film, while external oxidation layer mainly contained (Ni,Mn)Cr2O4. The bilayer structure was not found on the surface of Inconel 740H and Haynes 120, which indicated that the oxide structure was related to chromium content, as well as content and behavior of additional elements including cobalt element. High temperature corrosion resistance of four superalloys was as follows: Haynes 120 > Inconel 740H > Haynes 625 > Haynes 617. Compared with previous studies, S is not found in the corrosion products, which indicates that sulfides come from atmosphere of SO2 but not sulphate in coal ash.