As-grown Sr2SiO4:Eu thin films on Si (100) substrates have been reduced by hydrogen plasma reaction which was carried out by using radio frequency plasma enhanced chemical vapor deposition system. The photoluminescence spectra, the crystal structure and the surface morphologies of the plasma-reduced films were measured and compared with those of the as-grown films. At as-grown state, Eu3+ and Eu2+ ions co-exist so that the photoluminescence spectra of the films reveal several emission bands between 350 and 650 nm. They were due to f-f and f-d transitions within Eu3+ and Eu2+ ions. After the plasma-reduced process, the photoluminescence spectra of the films show a remarkable increase of blue-green emission from the transitions of Eu2+ ions and decrease of red emission from the transitions of Eu2+ ions.