The invention provides a preparation method of a titanium dioxide / active carbon composite nanofibrous membrane, characterized by comprising the following specific steps: dissolving polyacrylonitrile powder in N, N-dimethyl formamide; mixing titanium hydroxide gel with the polyacrylonitrile solution to obtain electrostatic spinning stock solution, and performing electrostatic spinning to get the composite nanofibrous membrane; placing the composite nanofibrous membrane in an electrically heated drying cabinet for being pre-oxidized; soaking the composite nanofibrous membrane in phosphoric acid or potassium hydroxide solution, washing the solution to be neutral by distilled water, and drying the composite nanofibrous membrane in the drying cabinet; and then, under nitrogen protection, heating up to 450-550 DEG C, and cooling to room temperature to get the titanium dioxide / active carbon composite nanofibrous membrane. The preparation method improves combination firmness between fibers and active ingredients of a photocatalyst, and also improves charge capacity of the fibers; the titanium dioxide / active carbon composite nanofibrous membrane is high in photo catalytic activity, good in absorption effect, reproducible and simple in a reproduction method, and can use sunlight, so that operations are easy and operation cost is low.