During the process of plasma enhanced chemical vapor deposition, the growth rate of microcrystalline silicon films must be improved to reduce manufacture cost. With the increase of growth rate, the photoelectrical properties of such films will be greatly decreased. The main cause is the diffusion length of the precursors on the film surface decreases. In this study, a quantitative kinetic model was developed and the reaction balance equations of SiH3 and H were constructed, and the deposition rate, diffusion length and their influencing factors were obtained. We find that the deposition rate is determined by the fluxes of both SiH3 and H. The diffusion length of precursors is determined by the substrate temperature and the configuration of the surface silicon-hydrogen bonds. The diffusion length has a higher value when the growing film surface is covered by mono-hydrides, it has a smaller value when covered by tri-hydride, and it has a value close to zero when covered by dangling bonds.