The invention provides a curing agent and a curing method for heavy metals in fly ash from mswi (municipal solid waste incineration). The curing agent comprises an aluminum-rich high-silicon material and an alkaline exciting agent, wherein the mass of the aluminum-rich high-silicon material is 15% to 25% of the mass of the fly ash from mswi; the mass of the alkaline exciting agent is 3% to 5% of the mass of the fly ash from mswi. The curing agent adopts industrial waste residues, and raw materials are cheap and easy to obtain; according to the curing method, lots of calcium oxide, chloride and sulfide existing in the fly ash from mswi have a hydration reaction with the aluminum-rich high-silicon material to generate a C-S-H (calcium silicate hydrate), Friedel (calcium chloroaluminate) phase and Aft (ettringite) phase system; during the formation process of the mineral system, a solid solution is formed through ion exchange, a new phase is formed through coprecipitation, and a relatively strong stable constraint effect can be played on heavy metals through physical adsorption and coating, so that wastes can be treated by using wastes, and harmless treatment of the fly ash from mswi and resource utilization of the industrial waste residues are realized.