Abstract: The ash melting test and the techniques of DSC, XRD and SEM were used to investigate the effects of SiO₂ additive on the melting behavior of MSW (municipal solid waste) incineration fly ash. Additionally, the reaction activities of produced minerals were analyzed by using the CASTEP model. The results showed that the ash flow temperature was 1355 ℃ when the blending ratio of SiO₂ (BRS) was 29.14%, approximately 200 ℃ lower than the original fly ash. The increase of BRS tended to enhance AMT. XRD analysis indicated that wollastonite, pseudowollastonite, gehlenite, andradite, anhydrite and trikalsilite occurred in glass-ceramics. Molecular simulation showed that pseudowollastonite, gehlenite and andradite were refractory minerals due to the high formation energy. Wollastonite, anhydrite and trikalsilite were fluxing minerals and led to the lower AMT. When the mass ratio of SiO₂/CaO<1, excess Ca²⁺ was prone to combine with reactive oxygen to form pseudowollastonite, which had better thermal stability. When the mass ratio of SiO₂/CaO was close to 1, wollastonite, which was the main crystalline phase in glass-ceramics, was considered as fluxing mineral to make AMT reduction. The simulated results indicated that the formation energy of wollastonite (-41.67 eV) was lower than that of other minerals. Moreover, the ratio of reactive oxygen in wollastonite was up to 77.78%. When the mass ratio of SiO₂/CaO>1, a large number of amorphous SiO₂ and cristobalite (non-reactive oxygen species) resulted with AMT rise. The percentage change between active oxygen and non-active oxygen in melts was the internal cause of AMT.