In order to further explore the genesis of theTangwan uranium deposit，the gangue mianeral pyrite was the main study object. Based on the detailed field and indoor petrographic observation，the pyrite was divided into three period including four stages: early metallogenic period（pyⅠ）， main metallogenic period（two stage： pyⅡa、pyⅡb）and late- metallogenic period（pyⅢ）.Methods:EPMA and LA- ICP- MS technologies were used to conduct in- situ testing and analysis of major, trace elements and sulfur isotopes of pyrite at each stage. Results:The results showed that the Fe content of pyrite in Tangwan uranium deposit is 45.80% -46.80%, the S content is 51.85% -3.84%, and the n(S)/n(Fe) ratio is 1.96~2.03. The trace elements in pyrite were few in variety and low in content, some of which were lower than that of the test line. As, Se, Ag, Sb, Au, Bi and U were significantly enriched relative to the continental crust, and As content was the highest, with an average of 1587×10-6. Co/Ni values range from 1.07 to 59.13. The total amount of rare earth elements was low and the main mineralization period was relatively high. The REE of pyrite in each period showed a similar distribution pattern, which highly similar to granite surrounding rock, and the negative europium anomaly is obvious (Eu is 0.12~0.44). The δ34S values of pyrite was -3.1%～-19.9%, pyⅠ, pyⅡa, pyⅡb, and pyⅢ showed a significant decrease followed by an increase. Conclusions:Based on the above geochemical characteristics, it’s considered that pyrite in Tangwan uranium deposit was rich in As and deficient in S, which was favorable for uranium mineralization. Each period pyrite belongs to the medium to low temperature magmatic hydrothermal origin, and its material comes from the granite surrounding rock. Combining the geochemical characteristics of pyrite in different stages, the geological characteristics of the deposit and the theory of uranium mineralization, it is considered that the ore- forming fluid of Tangwan deposit from the early metallogenic stage, the main metallogenic stage to the late metallogenic stage consistently shows a relative reduction environment, and has undergone the evolution of relative oxidation reduction and relative oxidation, and the mineralization temperature has gradually decreased. Pyrite played an important role in reducing the precipitation of uranium in the fluid．