The corrosion behavior of Inconel alloy 740H in simulated Coal-Ash / Flue-Gas Environment was investigated with high temperature corrosion test for 500 h at 850 °C. The weighing method, SEM (Scanning Electron Microscope), EDS (Energy Dispersive Spectrometer) and XRD (X-Ray Diffraction) analyses were employed to understand the corrosion kinetics, morphologies, compositions and phases of the corrosion products, respectively.The results indicated that the mass gain of Inconel alloy 740H was an approximately stable up to 500 h. After corrosion for 100 h, a continuous oxide scale identified as Cr2O3 and MnCr2O4 spinel formed on the surface of Inconel alloy 740H. Below the oxide scale, Cr depletion region was found and a large amount of inner corrosion products Al2O3 and Ti-rich were also observed. After corrosion for 500 h, the thickness of oxide scale and the corrosion depth increased obviously with the corrosion time increasing. The inner corrosion products was composed of Al2O3, Cr2O3, MoS and Ti-rich and distributed along the grain boundary. The corrosion mechanism of Inconel alloy 740H was also discussed based on the experimental results.