The purpose of this study is to improve the resource utilization rate of flue gas desulfurization gypsum, and to explore the effect of flue gas desulfurization gypsum content on the hydration characteristics of supersulfated cement co-activated with calcium aluminate and carbide slag. The effect of flue gas desulfurization gypsum on the hydration mechanism and performance evolution of supersulfate cement was revealed by mechanical property test, hydration product analysis and microstructure characterization. The results show that the compressive strength of supersulfated cement continues to increase with the increase of flue gas desulfurization gypsum content. When the flue gas desulfurization gypsum content increases to 20% (mass fraction), the compressive strength reaches the maximum value. In the early hydration stage, flue gas desulfurized gypsum reacts rapidly with calcium aluminate to form ettringite. Carbide slag provides an alkaline environment, promotes the dissolution of slag, and accelerates the reaction of slag and flue gas desulfurized gypsum to form a large amount of ettringite. At the same time, the formation of hydration products such as calcium silicate hydrate and hydrotalcite accelerates the development of early strength in coordination with the above reactions. In the later hydration, with the gradual consumption of flue gas desulfurized gypsum, the formation rate of ettringite decreases, and calcium silicate hydrate gradually transforms into the main hydration product, continuously improving the strength of matrix.