Microcrystalline silicon thin films were prepared by hot wire chemical vapor deposition with hydrogen dilution. Structures of the films were examined by Raman scattering, Fourier transform infrared (IR) and small angle X-ray scattering (SAXS)etc. It is shown that with increasing flow ratio RH=H2/(H2+SiH4) the volume fraction of crystalline increases while the hydrogen content decreases. The result from SAXS indicates that with increasing dilution ratio, the density of the film is increased, which implies the volume fraction of micro-voids is reduced. Combining with the data from IR and SAXS, we conclude that SiH2 vibration mode in hydrogenated microcrystalline silicon thin film is located at the grain boundaries rather than in the internal surface of the micro-voids.