<p>The corrosion mechanism of municipal solid waste incineration (MSWI) fly ash on magnesia-chromium refractories from the perspective of substance migration and transformation was investigated by using corrosion test at 1400 ℃. XRD, XRF, and SEM-EBSD characterization and thermodynamic software FactSage analysis were utilized. Although thermally stable compound MgCr₂O₄ can be formed in the refractories mitigating the corrosion, the SiO₂ in the fly ash can convert MgCr₂O₄ to Mg₂SiO₄ (forsterite) and MgSiO₃.The regeneration and transformation of MgCr₂O₄, as well as the low melting point and volume expansion properties of Mg₂SiO₄ and MgSiO₃, are responsible for the loosening of the refractory structure and the migration of magnesium from the refractory into the ash. When the refractory was corroded by MSWI fly ash repeatedly, the migration of the corrosion products from the refractory to the ash was the key to aggravate the corrosion. Increasing CaO content can mitigate the corrosion and magnesium migration by alleviating the formation of Mg₂SiO₄ and MgSiO₃.</p>