High-temperature incineration is the predominant method for managing municipal solid waste, enabling effective heat and heavy metal recovery and facilitating efficient energy and resource recycling. Fly ash generated from municipal solid waste incineration contains various heavy metals, chloride salts, dioxins, and other harmful substances, seriously impacting the ecological environment and human health. Vacuum melting treatment of fly ash effectively eliminates heavy metals and chloride salts, rapidly decomposes dioxins, and significantly reduces fly ash toxicity. This study optimized the temperature, vacuum level, and holding time for vacuum melting treatment, identifying the optimal conditions of 1400 ℃, 100 Pa, and 3.0 hours. The total chlorine removal efficiency reached 92.00%, and the soluble chlorine removal efficiency reached 96.85%. XRD phase analysis revealed that NaCl and KCl disappeared, while crystalline phases of Ca, Si, and Al minerals appeared under optimal conditions. The removal rates of various heavy metals increased significantly, with removal efficiencies of 81.34%, 89.26%, 90.86%, and 88.00% for Cu, Zn, Pb, and Cd, respectively. SEM imaging of fly ash treated under optimal conditions showed a uniform and smooth surface, indicating a transformation to a molten glass state. The DTPA method was used to assess the heavy metal toxicity. Results showed that the concentrations of Cu, Zn, Mn, and Ba in the treated samples were 48.51, 92.41, 51.93, and 48.52 mg/kg, respectively. The toxicity of heavy metals (as measured by EDTA extraction) decreased significantly compared to the original fly ash, although some ecological risks remain. After vacuum melting treatment, dioxin content and toxic equivalents were significantly reduced, with an overall emission reduction exceeding 96%. This study provides crucial insights for the vacuum melting disposal of fly ash, offering technical parameters and practical guidance for its safe disposal and resource utilization. However, this study only examined the phase characteristics of fly ash but lacked a comprehensive analysis of pollutant migration and transformation mechanisms. Further research should focus on the efficient resource utilization of the post-melting slag and investigate the mechanisms and kinetics of pollutant migration and transformation to develop more effective control strategies and technologies.