The potential release of Pb, Zn, Cr, and Cu in municipal solid waste incinerator (MSWI) fly ash was investigated by batch leaching experiments using sodium acetate solution as the extractant. The concentrations of heavy metals decreased against the increase of liquid-to-solid (L/S) ratio with the exception of Zn. In the case of low L/S ratios, the concentration of Pb and Zn was relatively high. Leaching solvents with a wide pH range (2, 4, 6, 8, 10, and 12) were used to determine the acid neutralizing capacity of MSWI fly ash. The concentrations of heavy metals declined evidently along with the increase of initial pH of leaching solvent when the L/S ratio was fixed at 20. The turning point appeared at the pH value close to 6. When the pH value was higher than 6, the concentrations of heavy metals remained at a low level. Sequential extraction tests were also performed to reveal the long-term leaching behavior. The results showed that Pb, Zn, Cu, and Cr were mainly present in the last three fractions, which were Fe-Mn oxides, organic matters bound and residual fractions and their leachability could be well-controlled in common natural environment. However, the long-term leaching risk would be increased with the presence of reducing agents and the change of the pH value of the surrounding environment.