Three-dimensional molecular dynamics simulations of epitaxial growth of aluminum film on substrates of nano pillar crystal array have been carried out. The embedded atom method (EAM) potential was employed for computing atomic interaction in aluminum. The results show that，the nano pillar crystal array substrate can release the misfit strain in the epitaxial film without forming any misfit dislocations，achieving a high quality epitaxial crystal film. However，two conditions must be met: 1) the cross sectional size of pillar crystal should be larger than the critical size of thermal stability，which is 19nm for aluminum at 700K；2) the height-space interval ratio of pillar crystals should be higher than 076. The latter ensures that the epitaxial layers on the neighboring pillar crystals can bridge with each other，and form a continuous film free of misfit dislocations.