The work aims to study the corrosion behavior of S30432 and HR3C coated with power plant coal ash and synthetic coal ash in the simulated boiler atmosphere at 700 ℃, to obtain the corrosion acceleration ratio of synthetic coal ash to the power plant coal ash and analyze the corrosion mechanism of two kinds of materials. The S30432 and HR3C steel samples coated with coal ash were placed in simulated boiler environments with 0.3% SO2 for 2000 h and then taken for weighing after certain interval, to obtain the corrosion kinetics curves. After 2000 h of corrosion, the corrosion products on the surface of the sample were cleaned to obtain the weight loss of the sample, and samples surface were cleaned and the weight loss of the samples after corrosion was obtained. The obtained by weighting samples at intervals. After 2000 hours of corrosion, the corrosion the corrosion acceleration ratio of the materials in synthetic coal ash and the power plant coal ash was calculated. The composition, morphology and structure of the corrosion products were analyzed by XRD, SEM and EDS. The corrosion products were identified as Fe2O3, Cr2O3 and FeCr2O4 when S30432 and HR3C were coated with the power plant coal ash. The main residual corrosion products were FeCr2O4 and FeS when S30432 was coated with synthetic coal ash. However, the corrosion products formed on the HR3C were Fe2O3 and Cr2O3 under the same condition. A thicker corrosion layer with many pores and cracks formed on the sample surface were observed when S30432 and HR3C were corroded in the the power plant coal ash. The corrosion layer formed on the S30432 and HR3C were almost spalled completely when the sample was coated with sythetic ash. HR3C shows much better corrosion resistance than that of S30432 because of the higher content of Cr and Ni. Due to the high content of sulfate in synthetic coal ash, synthetic coal ash obviously accelerates the corrosion rate of S30432 and HR3C. When S30432 and HR3C are corroded in the synthetic coal ash and the power plant coal ash, the acceleration ratio is 3.03 and 3.28, respectively.