Abstract: The self-diffusion behavior of oxygen near Σ5 symmetrical grain boundary in PuO₂ was studied with molecular dynamics. The results show that the self-diffusion ability of oxygen is effected and improved by grain boundary in a big extent, the diffusion ability of oxygen decreases with the increment of distance between oxygen and grain boundary interface, and the diffusion of oxygen near grain boundary is anisotropic and its ability is weaker along grain boundary interface than that perpendicular to grain boundary interface.