Abstract: TCLP experiment has been performed to study the relationships between liquid-to-solid ratio (L/S), initial pH value, extraction time and leaching characteristics of heavy metals (Pb, Cr, Cd, Ni, Cu, Zn) in fly ash from a coal and MSW(municipal solid waste) co-firing fluidized bed incinerator. The results suggest that the leaching weight of heavy metals increases with the rise of L/S, in which the leaching weight of Cr and Cu increases in most cases, but the leaching weight of Cd, Ni and Zn changes slightly when L/S exceeds 20. The leaching behavior of Pb is special, for its leaching curve has obviously a wave crest and a wave hollow. The leaching concentration of heavy metals at initial pH≤2.90 is larger greatly than that at initial pH≥4.03. With the increase of extraction time, the leaching concentration of Pb, Cr and Zn decreases, but that of Cd and Ni increases in general. The leaching concentration of Cu increases first, and then reduces. Among the three factors which are L/S, initial pH and extraction time, the effect of initial pH on heavy metals leaching is the largest. Heavy metals leaching from fly ash is more easily in acidic liquor than in basic liquor.