Under the background of the “carbon peaking and carbon neutrality” goals, the improvement and resource utilization of industrial solid waste and waste soil have become increasingly important. High carbon emissions are generated during the production of traditional cement and lime-modified solidifiers, which exhibit poor crack resistance and tensile properties. In contrast, a composite organic-inorganic membrane can be formed by waterborne epoxy resin combined with C?S?H gel in cement soil to cement the internal flaky or spherical soil particles, thereby improving the tensile strength and water erosion resistance of the soil. In this paper, slag and desulfurization gypsum were selected as cement admixtures, and waterborne epoxy resin was added to improve the water resistance. Accordingly, a new water-resistant solid waste-based solidifier combining inorganic and organic materials was prepared to improve soft soil. The results indicate that when the mass ratio of cement to slag to desulfurization gypsum is 4∶2∶0.5, the strength of the inorganic solid waste-based solidified soil material reaches its maximum. In addition, the optimal dosage of waterborne epoxy resin is approximately 15% of the dosage of the inorganic solidifier. When this dosage is exceeded, the hydration process is hindered by the excessive polymer membrane, adversely affecting the strength of the solidified soil.