The grain boundary and dislocation motion characteristics on the atomic scale are significant for the study of material failure mechanisms. In the present work, by theoretical analysis and numerical simulation, the most stable phase of Fe crystal under given conditions is confirmed. Distribution of dislocation potential under different torsion angles is studied for BCC-Fe (001) twist grain boundary. The dislocation motion in Fe (001), Fe (110) and Fe (111) twist grain boundary under tension, compression and shear loading are also investigated.