Abstract: The reaction of U(UO_2) with O_2 and CO_2 was studied by temperature programmed analytical technology. The experimental results show that there is an inducement-term in the reaction of U(UO_2) with O_2 and CO_2. The ignition temperature(T_0) varies between 581 and 606 K at different concentrations of oxygen(16%～45%), the major intermediate product is UO_2 and the final product is U_3O_8. The T_0 of carbon dioxide is higher than that of O_2 and the CO_2 dissociates into CO during the reaction. The results also indicate that the apparent activation energy reduces with increase of gas concentration.