Abstract: By means of molecular dynamics, diffusion behaviors of oxygen dumbbell interstitial defect in UO2 were simulated under the influences of tensile strain direction and tensile strength with different substrate temperatures. The diffusion of oxygen dumbbell interstitial defect is threedimensional, and the ability of diffusion is relation to substrate temperature and tensile strength. Using simulation results, the diffusion coefficient of oxygen dumbbell interstitial defect was conformed. From the simulation, oxygen dumbbell interstitial defect is always arranged in 〈111〉 direction during diffusion process, higher temperature and larger tensile strain, more obvious the diffusion becomes, especially with increasing tensile strength along 〈111〉 axial, the direction of diffusion is mainly along 〈100〉 axial under strain or not. The results provide the basis for the study to radiation damage effects in UO2.