Abstract: Based on the analyzing for crystal structure of nanometer titanium dioxide,the photocatalysis principle,preparing technique,modification and analysis methods of nano-TiO₂ were discussed.The difference of rutile type TiO₂ and anatase type TiO₂ in photocatalysis ability were presented.It was clarified that anatase type TiO₂ nano-crystal had better photocatalysis ability than rutile type TiO₂ since having more mass transfer interspace.Improvement of photocatalysis performance should be actualizde in terms of reducing the electric field tie of O to Ti.The newly research results of photocatalysis technique in different application field were introduced.