Melting process was used to convert hazardous heavy metals fly ash from municipal solid waste incinerator into useful products. Some parameters such as chemical composition, microstructure morphology, mineralogy, leaching characteristic, of slag melted from fly ash were investigated at 1100 to 1400 °C temperature (for 90 min). Good melting effects are achieved when the temperature at 1300 °C. It showed that the molten sample became full smooth, much hard in surface structure, while the section of the molten sample had lustrous or no apparent aperture. The raw fly ash had completely melted. Compared with the changes of chemical composition and melting effect by X-Ray diffractometry, for the raw ash and molten slag. The results indicated that the main crystalline phases of raw fly ash were halite, sylvite, quartz, calcite, anhydrite, larnite and mayenite. Samples with a high ratio have a crystalline matrix consisting of CaS, gehlenite, Ca-Al-silicates mellilite, anrothite and an interstitial glassy phase. The leaching test on melted slags samples showed that the fly ashes were successfully detoxified to meet of the limits toxicity characteristic leaching procedure (TCLP) in China and United States. After melting, the volatile heavy metals, like Cd and Pb were found in the gas collected, where Zn, Cr, and Ni were fixed into the melted slag. The concentration of heavy metal Zn, Cr, Pb, Cu, and Cd decreased distinctly. Thus, melting process is efficient for heavy metals stabilization in fly ash from municipal solid waste incinerator.