Abstract: The laser shock-induced phase transformation of iron with different volume voids has been investigated by means of molecular dynamics（MD）simulations. By comparing the perfect single crystal iron and the iron with different volume voids, the effects of the void volume have been presented. Simulation results show that the void decreases the phase transformation pressure, and the bigger void induces lower pressure; the increase of void volume speed up the nucleation and the expansion of transformation; the void also changes the initial nucleation district, and makes a butterfly shaped nucleation pattern. The influence of rarefaction wave in bigger void is stronger, which affects phase transformation nucleation sites, and brings on a lot of atoms with amorphous structures. The effect of void