The invention discloses a carbon nitride-modified titanium dioxide super-hydrophilic porous film as well as a preparation method and an application thereof. The method comprises the following steps: with dicyandiamide or tripolycyanamide as a precursor, calcining to prepare a carbon nitride nanosheet; dispersing the carbon nitride nanosheet in absolute ethanol so as to obtain a carbon nitride dispersion liquid, then adding a titanium dioxide precursor, diacetone and alcohol amine, uniformly stirring to obtain a uniform solution, dropwise adding the mixed liquid prepared from the absolute ethanol, water and acid into the uniform solution so as to obtain carbon nitride / titanium dioxide composite sol, aging for a period of time, coating the carbon nitride / titanium dioxide composite sol on a preprocessed substrate, carrying out drying and ultraviolet irradiation, so as to obtain the carbon nitride-modified titanium dioxide super-hydrophilic porous film. The carbon nitride-modified titanium dioxide super-hydrophilic porous film is prepared from the raw materials which are cheap and easily available, the preparation condition is easy to realize, and the film can be obtained without carrying out high-temperature calcining, so that the preparation coat of a super-hydrophilic film product is lowered, and the popularization and application of the technique is benefited.