Hydrogenated poly-crystalline silicon thin films are deposited by inductively coupled plasma assisted pulsed dc twin magnetron sputtering at a temperature below 300 ℃. The samples are characterized by X-ray diffraction, Raman scattering, transmission electron microscopy, and Fourier transform infrared spectroscopy. The relationship between hydrogen dilution ratio and the characteristic of thin film is studied systematically. The mechanism of crystallization is discussed on the basis of the results of diagnosis of plasma by Langmuir probe and optical emission spectra.