Abstract: The leaching characteristics of fly ash from municipal solid waste incineration (MSWI) in a flow-through system werestudied using column tests. The results from the leaching tests showed that: The pH of the extract increased at the beginning of the experiments and then decreased, and remained in alkaline condition (pH9.66) until the end of the experiments; The leaching process of main cations (Na⁺, K⁺, Ca²⁺) and anions (Cl^－, SO₄^2－) in the fly ash mostly happened at the beginning of the experiments (96 days), resulting in very high salinity in earlier lixivium; The leaching concentrations of four heavy metals (Cr, Pb, Cu and Cd) in the column leaching tests were much lower than those of the batch tests, and they were relatively high at the beginning of the experiment. Although the leaching concentrationsof the heavy metals obviously decreased when the leaching time was greater than120 days, the comparative heavy metals could be exuded continuously.