3C-SiC thin films were grown on Si(111) substrates at 1250 °C by horizontal low pressure chemical vapor deposition (LPCVD). We performed an exhaustive study on the effect of H2flow rate on the crystalline quality, surface morphologies, growth rate, n-type doping of 3C-SiC thin films and the voids at the interface. The films show epitaxial nature with high crystal quality and surface morphology increase obviously with increasing H2 flow rate. The growth rate and n-type doping are also dependent on H2 flow rate. The properties of the voids at the interface are discussed based on the cross-sectional scanning electron microscope characterization. Transformation of voids with increasing H2 flow rate are attributed to higher 3C-SiC film growth rate and H2 etching rate. The mechanism of void formation is discussed based on our model, too. The results demonstrate that H2 flow rate plays a very important role in the heteroepitaxial growth of 3C-SiC films.