Displacement cascade behaviours of body centred cubic (BCC) iron nanowires (NWs) with five different PKA directions has been investigated by using molecular dynamics (MD) simulation. MD simulation is performed by using a modified embedded atom method (EAM) potential at 300 K. It can be concluded that the number of Frenkel pairs (FPs) and clusters in [00 (1) over bar]/(001) and [00 (1) over bar]/1/2(001) direction in thermal spike stage are large due to the low displacement threshold energy in the < 100 > direction. The maximum number of point defects and clusters are in [01 (1) over bar ]1(001) direction and more than half of those defects are in [11 (1) over bar]/(001) direction in the stable quenching stage because the stable and metastable configurations of the self-interstitial atoms (SIAs) are along the < 110 > and < 111 > directions, respectively. In addition, the shape of vacancy clusters in [01 (1) over bar]/(001) direction is lamella-like in shape and different with the shape in other incidence directions, which contains two or three layers' vacancies and results in collapse of adjacent crystal.