The multiple cluster growth with fractal or compact morphology in ultra-thin films has been simulated with various permitted diffustion steps. It is shown that the fractal dimension increases with increasing cluster size in the fractal growth. The nucleation rate decreases with increasing diffusion steps and drops rapidly with increasing deposition time. The cluster size S can be described by a power law as S-(t-t0)κ, where (t-t0) is the growth time. The growth index κ is slightly smaller than 1 given by the classical nucleation and growth theory, due to the branching effect between clusters. A nonlinear phenomenon (i.e., the larger the cluster size, the larger the growth index κ) has been obtained.