Yunfu pyrite tailings have a huge storage capacity, which affects the surrounding environment and wastes resources. In this paper, the feasibility of high absorption utilization of tailings used as auxiliary cementitious materials was discussed, the mineral and chemical composition of tailings and the occurrence state and content of sulfur were analyzed, and the properties of tailings as auxiliary cementitious materials and the evolution of gypsum and pyrite contained in tailings and their influence on the properties were studied. The results show that Yunfu pyrite tailings belong to high sulfur pyrite tailings, and the sulfur in the tailings exists in the form of pyrite (FeS2), pyrrhotite (Fe1-xS) and gypsum. In the hardened cement paste, most of the gypsum in the tailings reacts to form ettringite (AFt) at 28 d, which is the main factor affecting the performance, and the oxidation degree of FeS2 is still low at 180 d. The 28 d activity index of cement mortar mixed with 30% (mass fraction) pyrite tailings can reach 74%, but compared with 3 d and 7 d, the 28 d activity index does not increase or even decrease, and the compressive strength at 180 d is inverted. It may be a better way to use tailings as cement mixture and coagulant at the same time.