A kind of compound additive was studied and prepared in the paper, which associated with many functions. Using typical fly ash of Shanghai and Fuzhou, We studied the effect of the additive on evaporation rate, flowing temperature, fixed rate of heavy metals and its leaching characteristics in melting slag in the process of melting fly ash. The result showed that the flowing temperature and the evaporation rate of fly ash could be respectively reduced approximately 150 degrees C and 10% - 20% by adding 10% additive, and the fixed rate of heavy metals Cu and Pb increased 10% - 20%, especially Zn, which could increase 40%. The amount of leaching heavy metals in melting slag were both under corresponding standard limits using either national toxicity leaching methods or TCLP of EPA.