A Molecular dynamics method with a Many-body Tersoff-type interatomic potential has been being applied to analyses of hydrogenated Amorphous silicon (a-Si:H) thin-film growth processes. As a first step toward film growth simulations, Molecular dynamics simulations of SiH3 radical, which would be a significant precursor for the a-Si:H thin-film growth processes, and a-Si:H formation with a rapid quenching method have been performed by developing new Tersoff-type interatomic potential between Si and H in this study. Visualization of SiH3 radical dynamics by computer graphics has made it possible to observe the inversion and rotation of SiH3 radical, which had been predicted by infrared diode-laser spectroscopie measurement in other group. In addition, visualization of the a-Si:H sample has helped us to find that there are some microcavities in the sample and that there are two kinds of hydrogen in the sample, gathering closely together while lying scattered, which had been predicted in IR absorption experimental results.