Kinetic Monte Carlo simulations are carried out to explore the growth of the Ag ultrathin film on Pt (1 1 1) in the early growth stage. With increasing temperature, the island shapes are demonstrated to transform from fractal to compact and resemble the surface crystal structure at high temperature. The transition temperature of the island evolution is demonstrated to increase with the deposition rate. The competing mechanism between nucleation and growth is pursued. The transition temperature of island evolution is deduced by the average island density distributions and demonstrated by the island morphology evolutions. In addition, the extent of a non-ideal substrate surface is explored. As the interaction energy. between adatom and defect point increases, the island shape becomes small and irregular. The effect of surface defect on the nucleation and growth is demonstrated. (C) 2014 Elsevier B.V. All rights reserved.