Interfaces are good traps for implanted He and radiation induced damage, and understanding the role of interfaces is important for designing highly radiation-resistant materials. In this article, Nb sheet and Nb film on MgO substrate (Nb/MgO) are irradiated by He ions, and it is found that the He bubble distribution along radiation depth between Nb sheet and Nb/MgO film is different. The comparison reveals that this difference is resulted from the diffusion of He atoms driven by strain gradient in Nb film close to Nb/MgO interface. This study could provide novel mechanisms for further understanding the interface enhancing radiation tolerance.