Abstract: To enhance the resource utilization of industrial by-product gypsum and reduce dependency on and consumption of natural sand and gravel resources, this study used desulfurized building gypsum, slag and fly ash as the main raw materials to prepare gypsum-based sandless self-leveling materials. Experimental results showed that slag and fly ash effectively improved the flowability and reduced the relative linear expansion rate after initial setting. Differences in particle size, composition, and surface activity between slag and fly ash led to variations in the timing of the maximum heat release rate during the hydration acceleration phase. However, both admixtures reduced the maximum heat release rate and cumulative total heat release. The filling effect of slag improved the pore structure of the gypsum, reduced porosity, and increased the number of micropores in the 0-0.1 μm range, thereby densifying the matrix structure and enhancing the material's strength. As the fly ash content increased, the number of pores in the 0.1-10 μm range increased, resulting in a gradual decrease in strength and water resistance. This study provides valuable insights for the practical application of gypsum-based sandless self-leveling materials and promotes the resource utilization of industrial by-product gypsum.