Through study of the preparation of TiO2 porous film by anodic oxidation, the forming mechanism of the porous film is put forward. Porous TiO2 film is prepared on the surface of pure titanium (TA1) in sulphuric acid electrolyte by constant voltage and constant current anodic oxidation respectively, with pure titanium as anode and copper as cathode. The pore size of the porous film is about 100 nm~200nm by observation of FESEM. It is indicated that the pore size distribution has a trend of augment with the increasing of the anodization voltage or the current density. Furthermore, the forming mechanism of TiO2 porous films in sulphuric acid is discussed.