The Si-doped glow discharge polymer (Si-GDP) films are deposited by glow discharge polymerization technology at different pressures. The structure and the composition of eath Si-doped glow discharge polymer film are characterized by the Fourier transform infrared spectroscopy and x-ray photoelectron. Using ultraviolet/visible spectroscopy, the optical band gap is analyzed. The results show that the Si element exists mainly in the form of Si—C, Si—H, Si—O, Si—CH3. The relative content of Si—C decreases and then increases with the increase of pressure. It can be found that the ratio between C—C and C C decreases with the increase of pressure. As the pressure increases, the optical band-gap decreases and then increases.