In order to solve the problem of unstable calcium sulfite, the main component of sintering exhaust gas desulfurization ash, the catalytic decomposition effect of desulfurization ash is studied by using a boiling furnace, in which the catalyst is a composite catalyst composed of ferrous sulfide and ferrous sulfate. The effects of composite catalyst ratio, holding time, reaction temperature, gas flow rate and other factors on the desulfurization rate and roasting products of desulfurization ash in the boiling furnace are discussed through the thermogravimetric analysis of the catalytic decomposition process of desulfurization ash. The thermogravimetric results show that the decomposition temperature of desulfurization ash is reduced by about 100 °C after the addition of composite catalysts. The boiling furnace test shows that when the reaction temperature is 900 °C, the gas flow rate is 3 000 mL/min, the composite catalyst ratio is 2.5:1 and the holding time is 30 min, the desulfurization rate can reach 91.41%. The SO₂ generated by the catalytic decomposition of desulfurization ash can provide raw materials for the subsequent manufacture of sulfuric acid, and the roasting product can be used as raw materials for sintering plants, effectively solving the environmental pollution of desulfurization ash.