The invention provides a preparation method and an application thereof for a vanadium pentoxide/oxidized graphene composite film, and relates to the technical field of composite nano-materials. The preparation method comprises the following steps of (a) preparing a vanadium pentoxide aqueous dispersion; (b) preparing an oxidized graphene aqueous dispersion; (c) preparing a suction filtrate; (d) preparing a precursor of a vanadium pentoxide/oxidized graphene composite film; (e) preparing the vanadium pentoxide/oxidized graphene composite film. According to the technical scheme of the invention, the technical problems in the prior art that, existing preparation methods are complicated in process and prepared vanadium pentoxide/oxidized graphene composite films are poor in uniformity and are difficult to be applied to flexible energy-storage devices can be solved. The vanadium pentoxide aqueous dispersion and the oxidized graphene aqueous dispersion are mixed up, so that a flexible vanadium pentoxide/oxidized graphene composite film can be prepared through the pressure-reduced suction and filtration method, wherein the method is easy to control and operate. Meanwhile, the prepared vanadium pentoxide/oxidized graphene composite film can be applied to flexible capacitor devices. Therefore, the problem that the materials of traditional processes are hardly applied to flexible energy-storage devices can be solved.