NOVELTY - Manufacturing a crystal titanium dioxide nano rod array thin film, involves washing metal titanium base plate in acidic washing liquid, washing the plate using deionized water, immersing the plate in reaction liquid formed using nitric acid, melamine and hydrogen peroxide to obtain a titanium dioxide nano linear array thin film, fetching reacted titanium base plate, washing plate using de-ionized water, placing the plate in hot water, regulating pH of hot water, reacting, fetching plate out, washing the plate using de-ionized water and drying the plate.    USE - The method is useful for manufacturing a crystal titanium dioxide nano rod array thin film used in photocatalysis, photoelectrocatalysis, thin-film solar cell, gas sensor, and biological material.    ADVANTAGE - The method is simple, and completely prevents the growth of the particles and the reduction of the specific surface area during the post thermal treatment process. Template and catalyst are not needed during the preparation process. The method causes no pollution, is inexpensive, firm in combination between the thin film and the titanium base plate, and has excellent crystallization degree and high photocatalytic activity.    DETAILED DESCRIPTION - Method for manufacturing a crystal titanium dioxide nano rod array thin film, involves (a) mixing hydrofluoric acid (in %mass) (50-55), nitric acid (65-68) and de-ionized water in a volume ratio of 1:3:6 to prepare acidic washing liquid, (b) adding nitric acid (0.34-0.45 M/l) and melamine (0.016-0.024 M/l) to hydrogen peroxide solution (20-30) to obtain reaction liquid, (c) washing a metal titanium base plate in the acidic washing liquid, ultrasonically washing the plate using deionized water, immersing the plate in the reaction liquid obtained in the step (b) to react for 60-72 hours at 60-80 degrees C to obtain a titanium dioxide nano linear array thin film, and (d) fetching the reacted titanium base plate, washing the plate using the de-ionized water, placing the plate in hot water at 60-80 degrees C, regulating the pH value of hot water to be 1.3-4.0 using hydrochloric acid, reacting for 20-72 hours, fetching the plate out, washing the plate using the de-ionized water, drying the plate, and finally, obtaining the crystal titanium dioxide nano rod array thin film.