The invention discloses a making method of nanometer porous thick film of titanium oxide, which comprises the following steps: (1) adopting dilute nitric acid to disperse TiO2 nanometer particle; (2) blending the powder, water and pore former into spread coating slurry; (3) coating the TiO2 slurry on the substrate through glass rod; blowing; (4) repeating the coating for several times until the needed thickness; (5) proceeding high-temperature heat disposal; adopting P-25 nanometer powder of Degussa company as the TiO2 powder, the carbowax as pore former, the glass (quartz glass, ITO or FTO conductive glass), monocrystalline silicon, sapphire and other materials as substrate. The thickness of the TiO2 film is controllable between 1 and 30um with grain size about 20-30nm, which simplifies the making method with cheap cost for large-scale manufacturing.