Density functional theory calculations have been used to investigate the mechanisms of dissociative adsorption of methylsilane (CH3SiH3) on the Si(100)-2 x 1 surface. Three different reaction pathways via Si-H, C-H, and Si-C dissociation are used to describe the formation of -SiH2CH3, -CH2SiH3, -CH3, -SiH3, and -H fragments adsorbed on the dimer dangling bonds. The geometry, energetics, and vibration properties of the critical points along the potential energy surface using the Si9H12 one-dimer and Si15H16 two-dimer cluster models are investigated. Our results indicate that the product of Si-H dissociation is the dominating dissociative product. The results also show that methylsilane is a good candidate for the growth of SiC films.