In this paper, molecular dynamics method has been employed to model mode I crack propagation in body center cubic (BCC) single iron crystal. To maximize the simulation efficiency the parallel computing was performed. Six cases with different lattice orientations have been simulated to investigate the crack propagation behaviors at atomic level. The strain distributions have been calculated to indicate the density of dislocation. It has been found that the lattice orientation significantly affects the propagation behaviors. The crack in BCC iron propagates more readily along the direction <111> on the plane {1-10}.