After mixing municipal solid waste incineration fly ash (MSWIFA) with silica fume and a certain proportion of deionized water, natural curing, steam curing and thermal treatment were performed respectively to stabilize heavy metals. The effects of additive amounts of silica fume on the leaching of critical heavy metals in MSWIFA with natural curing and steam curing were studied. Specification distribution of heavy metals, crystal structures and microstructures of steam curing samples and thermal treatment samples were also investigated. The results showed that the leaching concentrations of Pb, Cd, Cr and Cu gradually decreased with the addition of silica fume from 0% to 10% while using natural curing and steam curing. When adding 10% silica fume, the leaching concentration of Pb, Cd, Cr and Cu for natural curing samples were slightly higher than that for steam curing samples, in which specification distribution of heavy metals did not show significant change as compared with that in raw fly ash. Highly effective heavy metal stabilization of thermal treatment for Pb, Cd, Cu and Zn could be achieved, proven by leaching test results and specification distribution of heavy metals. The ratios of residue state of Pb, Cd, Cu and Zn in fly ash after thermal treatments increased from 37.12%, 11.82%, 44.30% and 51.94% to 84.75%, 75.49%, 77.20% and 67.40%, respectively, while the ratios of acid soluble state decreased from 3.99%, 54.92%, 6.56% and 10.49% to 0.44%, 9.37%, 2.72% and 3.59%, respectively.