Pyrite is a sensitive mineral in the geological environment, and its oxidation produces an important geochemical and environmental effect on the control of the redox and pH conditions. Column experiment results were used for modeling the geochemical processes in uranium mill tailings under lcaching conditions. Oxidation of pyrite dominates the control of the tailings leaching process. The experimental and modeling results show that the leachate chemistry changes substantially with the decrease in pyrite consumption. In the initial stage of the leaching experiment, the pyrite is consumed several hundred times greater than that in the later stages, for much more oxygen is present in the tailings in the initial stage. As the experiment continues, the tailings is gradually saturated with water and the oxygen concentration greatly decreases and so does pyrite consumption. The experimental and modeling results are useful for the design of mill tailing decommissioning., oxidation process and transport of radioactive nuclides and heavy metals can be constrained by controlling the oxygen concentration of tailings and the infiltration of meteoric water.