The evolution of crystal orientation of GaN films grown on graphene was investigated. Assisted with AlN nucleation layer, GaN was gradually merged with grains which had the same orientation of graphene from smaller polycrystalline grains. Finally, a GaN film with a thickness of about 4.6 μm was formed. EBSD and XRD have confirmed that the overall orientation of GaN becomes consistent, and Raman spectrum also shows the high crystalline quality of the GaN.