The invention relates to a C-based porous composite membrane and an application thereof. With a porous membrane prepared from one or more than two of organic macromolecule resins as raw materials as a matrix, a thin layer prepared from carbon black and the organic macromolecule resins is sprayed on the surface of the matrix to prepare the composite membrane; and the mass percent of the carbon black in the thin layer is 5%-60%. The composite membrane is simple in preparation method, environment-friendly in process, controllable in thin layer thickness and adjustable in ion selectivity. Compared with an original porous membrane, the composite membrane has better vanadium ion obstructing capabilities and ionic conductivity; and the assembled vanadium flow energy storage battery has relatively high battery performance.