The composite rapid soil stabilizer (CRSS) is a newly developed material for rapid curing of sludge with fast setting, fast hardening, and high strength properties. CRSS was used to solidify the sludge, and the durability test of the solidified sludge under the action of sulfate erosion was carried out to analyze the influence of erosion time and Na2SO4 and MgSO4 concentration on the physical and mechanical properties of the solidified sludge. The research results showed that as the erosion time increased, the mass of soaked samples increased gradually. Additionally, the strength of samples soaked in clear water continued to rise, while the strength of samples soaked in sulfate increased first and then decreased. After 112 days of erosion, the higher the concentration of SO42-, the greater the mass of the soaked sample and the lower the strength. At the same concentration, the mass of the soaked sample with MgSO4 was the largest, but the strength was the lowest. Under the action of sulfate attack, the soaked samples produced a large number of expansive products, and the cumulative pore volume first decreased and then increased. The microstructure of the MgSO4-soaked samples suffered the most damage due to the double corrosion of Mg2+ and SO42-. Based on the macroscopic and microscopic test results, the microscopic evolution mechanism of the durability of solidified sludge under Na2SO4 and MgSO4 erosion environments was revealed. The solidified sludge with CRSS has good sulfate resistance durability, which lays a theoretical foundation for the engineering application of CRSS.