Abstract: The reaction between uranium and steam was investigated using X-ray diffraction and Rietveld method in the report. In order to clearify the role of oxygen in the corrosion of uranium in steam, the surface crystal structure and corrosion kinetics of uranium in humid oxygen and humid helium gas were studied. The experiments were carried out in the XRK reactor accessary of Philips diffractometer. The experimental temperatures were 50 ℃ and 100 ℃ respectively. Rietveld refinement was performed by the X’Pert Plus software, which refined the structure parameters and gave the mass fraction of each component at the same time. The results indicate the dynamic expressions for the reaction between uranium and steam in humid oxygen are initially nonlinear, and turn to be linear subsequently. Whereas the content of oxide as a function of time is linear in humid helium. The absence of oxygen will accelerate the corrosion rate of uranium in the humid gas.