Abstract: Paste made from high-sulfur tailings shows strength deterioration to different degrees and this can cause great changes in the quality of the filling body. The deterioration and degradation mechanism of high-sulfur paste with different sulfur contents was analyzed using XRD (X-ray diffraction) phase analysis and an ESEM. The results showed that sulfur tailings promoted the growth of early strength to a certain extent, but inhibited the development of later strength, and the greater the sulfur content, the more obvious the effect. In addition, sulfate produced by sulfide oxidation can promote the formation of expansive ettringite and gypsum. Meanwhile, the acidic environment caused decalcification of C-S-H and dissolution of CH, destroys the cementitious system and further promotes the degradation of the filling body. The crystal expansion strain and crack development process were analyzed using a pore calculation model. The linear development of elastic strain in swelling material was clarified.