Si films were deposited by inductively coupled plasma chemical vapor deposition at room temperature with a mixture of SiH4/H2. The microstructure of the film was characterized with Fourier transform of infrared, Raman spectroscopy, atomic force microscopy. We found that SiH4 concentration strongly affects the structure of Si films and nano-crystalline film can be synthesized at room temperature by optimizing the silane concentration. The analysis for optical properties of the films suggested that the optical band gap EOPT of films are distinctively lower than those of amorphous Si films. It has been observed that the EOPT of sample decreases with the increasing of H content in film.