In situ-fabricated three-dimensional micro/nanostructure TiO2 films over titanium substrates possess advantages such as large specific surface area, high light efficiency, and good electron conductivity. Titanium substrates are ablated by femtosecond laser for fabricating micron structures. Then it is processed by chemical oxidation with H2O2 to form nanoporous TiO2 on the surface of micron structures. The average reflectance of the as-fabricated three-dimensional TiO2 structure is below 5 % over the ultraviolet wavelength range. The photocatalytic degradation of methyl orange shows that catalytic performance is largely determined by the size and morphology of the micro structures prepared by femtosecond laser. Additionally, the photo degradation rate remains constant over several consecutive cycles, which indicates that the micro/nanostructure TiO2 film is mechanically stable. The fabrication method of femtosecond laser combined with chemical oxidation can fully play advantages of ultraprecise on titanium substrate surface and controllable fabrication. The insights from the study on the fabrication of micro/nanostructure TiO2 film can be extended to guide the fabrication of other functional metal oxides on metallic substrates.