A new molecular dynamics (MD) code was developed to simulate the formation processes of ultrafine metal particles on substrate surfaces. In this methodology, the number of metal atoms deposited over substrate surfaces is increased one by one. The metal atoms are shot to the surface after regular time intervals with definite velocity. We applied this new MD code and computer graphics (CG) technique to the investigation of the formation processes of ultrafine Au particles on a MgO(100) plane at 300 K. The dynamic behavior of the Au atoms and the atomistic mechanism of the formation processes were revealed. The effect of deposition rates of Au atoms on the formation processes was also investigated. Decreasing the deposition rates of Au atoms was found to increase the number of fixed Au atoms on a MgO(100) plane. The effect of a groove in the MgO(100) plane was also investigated. It was revealed that surface defects greatly affect the configuration and location of Au clusters on the MgO(100) plane, in agreement with the experimental results.