In this work, microwave irradiation was introduced into a hydrothermal process to solidify heavy metals in MSWI fly ash. The reagent, Na2HPO4, showed a significant effect on the synthesis of zeolite-like materials, reducing the leaching concentration of heavy metals. The heavy metals morphologically transformed from acid-soluble form to a more stable form after treatment. Furthermore, the leaching concentration of all heavy metals reached the standard limit with 30 min curing.