Molecular dynamics (MD) simulation has been performed to study Helium (He) behavior and deformation feature of α-Fe with 0.1 at.% He injection. The effects of different pre-existing dislocation densities, temperatures and Cr concentrations were investigated in this study. Voronoi clusters (VCs) analysis and dislocation extraction algorithm (DXA) were performed to study the distribution of He clusters and the evolution of dislocations, respectively. The results show that He atoms are easier to segregate on pre-existing dislocations. Average size of He clusters is monotonically decreasing and total number is increasing with increasing dislocation density from 0 to 6.74 × 10 11 cm −2 . Furthermore, in tensile process, pre-existing dislocations accelerate the formation of larger He bubbles and these He bubbles enhance plasticity and promote dislocation multiplication. Higher dislocation density leads to higher yield stress, yield strain, and elongation stress. In addition, higher temperature (600 K and 800 K) can motivate He diffusion and improve dislocation mobility, whereas higher Cr concentration (9 at.% and 14 at.%) retards both of them. These increasing temperatures and decreasing Cr concentrations lead to decreasing yield stress, yield strain, but increasing dislocation density. All of these findings are helpful for understanding the atomic-level deformation process of He bubbles and dislocations evolutions in detail, which are elusive through experimental techniques. This will have profound significance for design and development of nuclear materials.