<p>Materials typically experience serious microstructure and performance degradations under irradiation in nuclear reactors. To explore radiation-resistant metals with high design flexibility is urgently requested for the safe application of nuclear energy. In this work, we discover an anti-radiation mechanism for this purpose in a gradient nanostructured nuclear grade austenitic stainless steel prepared by a flexible surface nano-crystallization approach. A special 3-dimensional microstructure network, consisting of low-energy grain boundaries, stacking faults, and dislocation networks, is introduced in the nanostructure, so that a large-scale adaptive martensitic transformation mechanism is activated under irradiation even at extremely high radiation doses and high temperatures. Consequently, the radiation resistance is significantly enhanced, while a superior mechanical property is retained, in nanostructured samples compared to coarse-grained counterparts. Results presented in this work thus explore a strategy to prepare radiation-resistant metals in future.</p>