This paper studied the characteristics of mineral and chemical phases of ferrum in the Zhiluo Formation of the Nalinggou uranium deposit in the northern Ordos Basin and the geochemical behavior of ferrum minerals in uranium metallogenesis process. The characteristics of mineral and chemical phases of ferrum and their metallogenic significance were investigated by means of optical microscopy identification, ferrum phases analysis, EPMA and pyrite S isotope analysis and so on,. The study shows that the ferrum phases in the sandstone include FeCO3 (siderite), FeS2 (pyrite), ferric oxide (hematite, limonite, magnetite) and ferric silicate (Biotite, chlorite and epidote), of which ferrum oxide is the most important form of Fe in sandstone of the Zhiluo Formation, and FeS2 is an important indicative mineral of mineralized sandstone. Mineralized sandstone has the highest contents of ferrum oxide and FeS2. The main uranium mineral in this area is coffinite, which has the closest relationship with pyrite, and occur mainly with pyrite in the form of “encirclement” and “inclusion”. Pyrite has δ34SV-CDT values from -39. 4‰ to -8. 5‰, showing the obvious enrichment of 32S and the depletion of 34S, indicating the characteristics of biogenic processes. The distribution characteristics of U/Th and δU indicate that the secondary reduced sandstone underwent obvious oxidation process and the reduction of mineralized sandstone was strongest. The characteristics of ferrum phases indicate the complexity of the metallogenic process of the Nalinggou uranium deposit, which not only includes the early oxidation and the later secondary reduction, but also involvement of microorganisms such as sulfate- reducing bacteria in the metallogenic process. Pyrite, the most sensitive indicator of uranium mineralization, was formed by the superposition of inorganic reduction and biological action.