Radiation-induced damage, especially the effect of He, has always been one of the crucial issues in future fusion reactors. It is thus essential to further understand the formation of He bubbles and hardening characteristics for future development of fusion application materials, for instance bcc-Fe as a simple model. Behaviors of crack propagation have been investigated in two different orientated cracks (001) and (121) of bcc-Fe models under different densities of He at 300 K by molecular dynamics simulation. The results show that these behaviors are tailored by crack orientations on the condition of non-He atoms: (001) orientated crack can be divided into elastic deformation, phase transformation and cleavage fracture of crack tip along phase transformation zone; however, (121) orientated crack is elastic deformation, stacking twin and after that formation and coalescence of voids to rupture. Furthermore, the yield stress and strain of (121)  orientated crack are higher than (001)  orientated crack, therefore (121) orientated crack has stronger ability to resist crack propagation. In addition, it is revealed that the influence of He density on the crack propagation exhibits two major aspects: when the density of He is lower (0.9%, atomic fraction), He can reduce the efficiency of phase or twin transformation and decrease the rate of crack propagation; when the density of He is higher (6.0%, atomic fraction), a large number of He clusters contribute to promote micro-voids nucleation, fracture mechanism for both crack models is the transformation of He clusters to voids, then voids coalescence, accelerating the occurrence of fracture. There is no twin or phase transformation in higher density of He.