WO3 films were deposited on glass substrates by magnetron sputtering at room temperature. Single factor method was employed to investigate the effect of sputtering parameters (sputtering power, oxygen flow and depositing time) on the photocatalytic properties of WO3 films. The crystalline structure and surface microtopography of WO3 film were characterized by X-ray diffraction and Scanning Tunneling Microscope respectively. The results show that the WO3 films are amorphous, and the photo-degradation rate of WO3 films for methylene blue reaches the peak value of 83.3% when the film was deposited under the conditions that the sputtering power was 80W, the oxygen flow was 15SCCM and the depositing time was 60min. The thickness threshold value for WO3 photocatalytic films is 632nm. When the thickness of the WO3 films is less than the threshold value, the photocatalytic degradation activity aggrandizes with the increase of film thickness, and then becomes steady when the thickness exceeds 632nm.