The present invention relates to a titanium dioxide photocatalysis air-cleaning film and its preparation method. It is characterized by that it utilizes the megnetron sputtering to form titanium dioxide photocatalysis air-cleaning film on the carriers of glass, metal and ceramics. It uses the direct synthesis of pure metal titanium target material and oxygen gas and utilzies are controlling powersupply to prevent pure metal target material from poisoning, in which the crystal grains formed by titanium dioxide film can be grown along the vertical direction or horizontal direction of carrier. The grain size is 10-100 nano, and the thickness of the film is 20-100 nano. Said titanium dioxide film is formed from single anatase phase or single rutile phase or their mixed phase, in which the anatase content is 50%-98% and rutile phase content is 2%-50%. Said film can effectively degrade harmful gases of formaldehyde and phenol, etc.