Abstract: This study analyzed the feasibility of utilizing waste incineration fly ash as an admixture in the production of sintered bricks. The analysis focused on the fly ash particle size and crystalline phase content, the mineral and chemical composition of the raw materials, material mixing ratios, surface quality and compressive strength of the finished products, the sintering mechanism, and the safety of the final products. Experimental results indicated that 85% of the fly ash particles had a diameter of less than 60 μm, with a relatively high content of glassy phase, which exhibited strong reactivity during sintering and reduced the sintering temperature. When the fly ash admixture content ranged from 10% to 20%, the sintered bricks exhibited good surface quality and compressive strength of MU20. At temperatures above 850 °C, numerous chemical reactions occurred, generating new crystalline phases such as mullite, effectively immobilizing heavy metals in the final products. Only a small amount of Zn leaching toxicity was detected in the finished products, which was significantly lower than the standard limit, while other heavy metals were not detected. Furthermore, the sintered bricks contained no dioxins. In summary, the utilization of fly ash could lower the sintering temperature of sintered bricks, resulting in products with excellent macro-performance and significantly enhanced heavy metal immobilization. This provides a novel approach for the resource utilization of fly ash.