Abstract: A combination of water washing pretreatment and thermal treatment may become a strategy for safe disposal and resource utilization of the MSW incineration fly ash. However， the influence of water washing on the migration and transformation of heavy metals has not been clearly studied， and the leaching risk of fly ash after disposal was underestimated by common leaching methods due to the strong buffering performance of fly ash. In view of the above problems， the curing mechanism of Pb， Zn and Cu in fly ash was studied， the influence of water pretreatment on the curing behavior of heavy metals was discussed. And a long-term leaching device with constant pH was designed to evaluate the long-term leaching behavior of fly ash after disposal. The results showed that the major product phases of Pb， Zn， Cu after the washing-thermal treatment were identified as lead-aluminosilicate， lead-calcium oxide， zinc silicate， zinc-aluminosilicate， etc. Meanwhile， the aforementioned phases were also detected in the scheme of only thermal treatment but with additional lead oxide chloride， lead aluminum oxide， lead silicate， zinc chloride and calcium copper oxide， etc. The types of Pb， Zn and Cu phases in fly ash after washing-thermal treatment were less affected by the sintering temperature and metal content. A higher Pb stabilization efficiency was obtained after washing-thermal treatment compared with only thermal treatmeat， with the value ranged from 94.59% to 99.60%. In the long-term leaching experiments with constant pH， the corresponding leachate pH of the two solutions were maintained in the range of 2.91~3.63 and 4.91~5.36. Leaching concentrations of Pb， Zn， Cu concentrations basically reached the maximum value after 600 mins， then decreased and maintained a low concentration at 0~0.09， 0.01~0.92， 0.03~0.22 mg/L（washing-thermal） and 0.03~0.31， 0.07~0.94， 0~0.11 mg/L （only thermal） respectively. The long-term leaching method proposed in this study could evaluate the long-term leaching risk of fly ash under extreme conditions， reveal the migration and transformation mechanism of heavy metals during the washing-thermal treatment process， and provide a reference for the safe disposal and resource utilization of fly ash.