The vitrification characteristics of municipal solid waste incinerator (MSWI) fly ash were investigated. Effects of temperature on the binding efficiency of heavy metals, the change of chemical compositions and the weight loss of fly ash in the range of 800 - 1350 ℃ were studied. Toxicity Characteristic Leaching Procedure (TCLP) of the United States was used to analyze the leaching characteristics of heavy metals in fly ash and molten slag. Results indicate that chemical compositions, the weight loss of fly ash and the binding efficiency of heavy metals in fly ash have a tremendous change in the range of 1150 - 1260 ℃. The percentage of CaO, SiO2and AI203 increases with the increasing temperature, whereas it is contrary for SO3 , K2O, Na20 and CI; especially when the temperature is 1260 ℃, the percentage of these four elements decreases sharply from 43.72%to 0. 71%. The weight loss occurs obviously in the range of 1150 - 1260 ℃. Heavy metals of Pb and Cd are almost vaporized above 1000 ℃. Cr is not volatile and its binding efficiency can reach 100% below 1000 ℃. Resuits of TCLP indicate that the heavy metal content of molten slag is beyond stipulated limit values.