Abstract: A super-large uranium deposit was discovered in Qianjiadian area of Kailu Basin. In order to define the influence of reservoir reducing agent on uranium mineralization, the authors defined the characteristics of reducing agent through the application of core, microscopic observation and related testing techniques. The results show that reducing agent in uranium reservoir in the study area is mainly in the form of organic-carbonized plant debris, hydrocarbons and pyrite. The pyrite in organic matter can provide a lot of high-quality reducing agent for uranium mineralization. The methane content and total amount of hydrocarbons in the mineralized sandstone are higher than those in other types of sandstone, and the ratio of gas hydrocarbon to heavy hydrocarbon increase obviously with uranium enrichment, indicating that uranium enrichment is also closely related to hydrocarbons. The common pyrite types in uranium reservoirs include raspberry pyrite, colloidal pyrite, idiomorphic pyrite and alloomorphic pyrite, which coexist with uranium in various forms as reducing agents. The TOC content and S content are generally higher, while Fe₂O₃/FeO ratio is obviously lower in sandstone with mineralized horizon. On the contrary, TOC content and S content are generally lower in the non-mineralized sandstone, while Fe₂O₃/FeO ratio is higher, indicating that uranium mineralization is positively correlated with TOC content and total S content, and is negatively correlated with Fe₂O₃/FeO. Therefore, the reducing agent is of great significance on restricting mechanism of uranium mineralization by the in-depth study on the characteristics of reducing agent in uranium reservoir, which provides theoretical guidance for the exploration and prediction of sandstone type uranium deposits.