The initial stages of the cubic indium nitride film growth at 350 degrees C were studied using low-pressure metal-organic chemical vapor deposition. The technique of the pre-deposition of indium was applied, that is, a layer of indium was first deposited on sapphire surface before the growth of InN. X-ray diffraction and X-ray photoelectron spectroscopy show that the pre-deposition of indium is able to promote the growth of InN films, and meanwhile, suppress the indium aggregation in the as-grown films. Atomic force microscopy images of InN films indicate that the pre-deposition of indium not only enhances the density of nucleate sites, but also facilitates the coalescence among the InN islands. The free energy calculations reveal that the pre-deposited indium atoms preferentially react with NH and N radicals after NH3 introduction, which leads to the formation of InN on the sapphire surface. The preferentially formed InN is then supposed to be responsible for the above phenomena.