Abstract: In this paper,304 austenitic stainless steel(AISI 304L)for nuclear industries was irradiated by argon ions,and the damage mechanism of its irradiation was studied.All samples were irradiated by 120 keV argon ions with the fluence of 1×10¹⁶cm^-2and 2×10¹⁶cm^-2respectively at room temperature.Then the microstructure of AI-SI 304L steel after irradiation was studied by transmission electron microscope(TEM).The result shows that small defect clusters such as voids,black spots,stacking fault tetrahedron(SFT),and larger defect clusters like dislocation loops were induced in irradiated AISI 304L steel.Meanwhile,with the increase of irradiation fluence,the size of dislocation loops and voids grew gradually.In addition,deformation structures like residual twins after annealing would turn into defect traps for trapping interstitial atoms,resulting in the increase of regional vacancy concentration and the dense precipitation of defect clusters at twin boundaries.