The saturation capacity and reaction probability of N2, CO2 and O2 adsorption on clean uranium surface at 323 K were quantitatively measured by the low pressure PVT method, and their reactivity and kinetics property were compared and analyzed. Results show that N2, CO2 and O2 exhibit the common reaction characteristics of adsorbed gas amount (coverage) approaching a maximum value and reaction probability decreasing with a rise in adsorbed gas amount. The reactivity ordering of gases with uranium is O2>CO2>N2 and saturation capacity follows the relation of NO2≈2.4NCO2≈7NN2. The initial reaction kinetics relies on the impacts of both product layer composition and thickness on the molecular dissociation and dissociative particles diffusion process, and the uranium nitride, carbide or oxycarbide have a stronger repression effect than uranium oxide on the above process.