NOVELTY - Preparation of titanium dioxide (TiO2) porous thin film includes preparing TiO2 nanocrystal sol by dissolving titanium salt into water, dripping ammonia, adjusting pH, standing and aging, filtering, redissolving precipitate into different solvents, dispersing by supersonic wave, dripping hydrogen peroxide, refluxing and heating, transferring ferrite titanium sol into high-pressure reaction kettle, crystallizing, filtering, and dispersing by supersonic wave; and coating directly the sol with 1 or 2 special profiles on a matrix.    USE - Method of preparing TiO2 porous thin film using TiO2 nanocrystal sol (claimed) for use in the fields, such as optical catalysis, photoelectric detectors, and solar cells.    ADVANTAGE - The TiO2 porous thin film has high crystallization degree, good dispersing ability, and controllable profile of sol. The surface of TiO2 porous thin film is flat and uniform, and has good adhesive force.    DETAILED DESCRIPTION - Preparation of TiO2 porous thin film includes:    (A) preparing TiO2 nanocrystal sol by using titanium salt as main raw material; dissolving titanium into water to form titanium salt aqueous solution; dripping ammonia under blending condition for complexing; adjusting pH to 7.5-8.0 to obtain white precipitate; standing and aging for 8 hours; filtering by pumping mode and washing; redissolving the precipitate into different solvents to obtain different crystallization products; dispersing for 0.5-1.0 hour by supersonic wave; dripping hydrogen peroxide (H2O2) to peptize in ice bath under blending condition; refluxing and heating for 4-6 hours at 78-100 degrees C to obtain ferrite titanium sol; transferring ferrite titanium sol into high-pressure reaction kettle; crystallizing for 8-15 hours at 100-200 degrees C; filtering by pumping mode; dispersing the filtered product into water by supersonic wave; and finally obtaining TiO2 nanocrystal sol; and    (B) at 20-80 degrees C, coating directly the sol with 1 or 2 special profiles on a matrix, by simple or alternative pore forming mode, to obtain TiO2 porous thin film, where coating is spinning coating or spray coating.