A series of silicon films at transition regime from amorphous to microcrystalline phase with different hydrogen dilution ratios were fabricated by the plasma-enhanced chemical vapor deposition (PECVD) technique, and the microstructural properties of the films at transition regime from amorphous to microcrystalline phase were studied using Raman scattering and Fourier transform infrared spectroscopy. The paracrystalline structure was used to elucidate the microstructure of silicon films at transition regime from amorphous to microcrystalline phase. The paracrystalline fraction (fp) as a signature of intermediate range order for the silicon films was proposed. The results indicated that the transition from amorphous to microcrystalline phase took place with the increase of hydrogen dilution. Silicon film grown just below transition edge was characterized by high hydrogen content, compact structure and enhanced medium range order, and hydrogen mainly passivated the surface of the film. Silicon film grown just above transition edge was characterized by low hydrogen content, high crystalline fraction and low interface phase, and hydrogen etching played an important role during film growth. The microstructure topography detected by scanning electron microscope verified the results from Raman scattering and Fourier transform infrared spectra. Silicon films had good microstructural properties at transition regime from amorphous to microcrystalline phase, especially around transition edge and were available as intrinsic layer for the thin film solar cells.