The tensile tests of body-centered cubic (BCC) Fe nanowires were simulated through molecular dynamics methods. The temperature and strain rate effects on the mechanical properties as well as the orientation-dependent plastic deformation mechanism were analyzed. For -oriented BCC Fe nanowires, as the temperature increased, the yield stress and Young’s modulus decreased. While the yield stress and Young’s modulus increased as the strain rate increased. With the increase in temperature, when the temperature was less than 400 K, the twin propagation stress decreased dramatically, and then tended to reach a saturation value at higher temperatures. Under different temperatures and strain rates, the -oriented Fe nanowires all deformed by twinning. The oscillation stage in the stress–strain curve corresponds to the process from the nucleation of the twin to the reorientation of the nanowire. For -oriented Fe nanowires, the plastic deformation is dominated by dislocation slip. The independent events such as the nucleation, slip, and annihilation of dislocations are the causes of the unsteady fluctuations in the stress–strain curve. The Fe nanowires eventually undergo shear damage along the dominant slip surface.