GaN films on Si substrates were obtained by hot-wall chemical vapor deposition and the growth condition during the process was investigated. The structure, surface morphology and the optical properties were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL). It indicated that hexagonal wurtzite GaN films were obtained on Si substrates. Preliminary results suggest that H2 as carrier gas play an important role at the same temperature in the growth of GaN films.