The generation of municipal and industrial waste has increased dramatically as the world has become more industrialized and urbanized. Municipal solid waste incineration fly ash (MSWI FA), as a by-product of waste incineration, contains heavy metals, dioxins, and other harmful substances, and its treatment has become an important challenge in the environmental field. This paper focuses on the co-treatment of MSWI FA with solid waste and provides an in-depth restudy of the treatment effects of different treatment methods on heavy metals and dioxins in MSWI FA. The findings demonstrate that a high-temperature thermal treatment method can effectively solidify heavy metals and prepare ceramic and glass by co-treatment with electrolytic manganese slag and municipal sludge. Meanwhile, the degradation rate of dioxin reaches more than 99%, but there are problems such as high energy consumption and difficult purification of flue gas. Non-thermal treatment methods solidify heavy metals through the synthesis of geopolymer cementitious materials. These methods utilize various solid wastes, such as phosphorus slag and nickel-iron slag, to achieve efficient immobilization while avoiding additional energy consumption. The resulting products can be recycled as valuable construction materials. The non-thermal treatment method, such as the mechanochemical method, can effectively degrade dioxins, but it needs to optimize the solid waste ratio. From a comprehensive point of view, solid waste co-processing of MSWI FA shows potential in reducing fly ash hazards and realizing solid waste resource utilization, but still faces challenges such as efficiency, cost, and solid waste compatibility. In the future, it will be necessary to further optimize the treatment process, develop long-lasting stabilizers, and strengthen research on the long-term stability and ecotoxicity of the products, in order to promote widespread use of this technology and help balance environmental and economic benefits.