Abstract: Austenitic stainless steels are widely used as the structural materials in reactors. However, due to its face centered cubic structure, austenitic stainless steels are highly susceptible to irradiation swelling. Swelling resistance is one of the most important topics for austenitic stainless steels used in nuclear reactors. In order to investigate the effect of helium on the evolution of bubbles and swelling, 316L stainless steel was first pre-implanted with 1 000 appm He at room temperature. And then it was irradiated by self-ion of 3.5 MeV Fe at 550 ℃ to a nominal dose of 26-65 dpa. He bubbles are not observed after helium irradiation at room temperature and after annealing at 550 ℃ for 90 h. The self-ion irradiation contributes to the bubble nucleation and growth. It is observed that high density of helium bubbles distributes in a depth of 300-1 000 nm after Fe-ion irradiation. Distribution of He bubbles is consistent with helium implantation plateau calculated by SRIM. No obvious He bubbles are observed in depth ＜300 nm and ＞1 000 nm, demonstrating the effect of helium atoms on bubble nucleation. The average size and number density of He bubbles in 100 nm depth bin were investigated. The average size increases in depth of 400-700 nm and reaches maximum in depth of 600-700 nm. In depth 700-900 nm He bubbles size decreases. The number density shows a slight decrease in depth of 400-900 nm. Meanwhile, the bubble size shows a unimodal distribution in depth of 400-500 nm and bimodal distribution in depth of 500-800 nm. The corresponding swelling increases in depth of 400-700 nm and decreases in depth of 700-900 nm, which is similar to the bubble size. As for the effect of radiation dose, the average size of He bubbles increases with increasing radiation dose, while the number density decreases slightly first and then increases. The average He bubble size increases from 3.3 nm to 9.7 nm when the irradiation dose increases from 26 to 52 dpa, and further increases to 11.9 nm when the irradiation dose increases up to 65 dpa. While bubble density decreases from 1.5×10²²/m³ to 0.8×10²²/m³ first and then increases to 2.0×10²²/m³. Pre-implanted helium accelerates the nucleation of He bubbles with density increasing and size decreasing. As a result, 316L stainless steel swells at a rate of 0.03%/dpa from 26 to 57 dpa, while swelling rate deviates to 0.26%/dpa when radiation dose increases from 57 to 65 dpa. The swelling behavior of 316L stainless steel after ion irradiation is consistent with neutron irradiation.