The invention discloses a polymer-modified ceramic-coated composite separator and an application thereof. The polymer-modified ceramic-coated composite separator comprises an organic separator base material, a ceramic layer and polymers, wherein the ceramic layer coats the surface of the separator base material and is 0.1-20 microns in thickness; the polymers grow in situ on the surfaces of the separator base material and the ceramic layer and inside the separator base material and the ceramic layer; the polymers are polymethyl methacrylate, polyvinylidene fluoride-perfluoropropylene, polyacrylonitrile, polyimide, polyether amide, or polyethylene oxide and the like ; the particle size of inorganic powder in the ceramic layer is 5nm to 10 microns; and the molecular weight of the material of the organic separator base material is 1,000-100,000,000. According to the polymer-modified ceramic-coated composite separator disclosed by the invention, due to the presence of the polymers, and the potential safety hazards caused by dusting and liquid leakage of the ceramic layer can be effectively reduced; the physical property and the electrochemical properties of the separator are effectively improved; meanwhile, due to the presence of the polymers, the interface stability between a separator electrolyte and an electrode can also be improved; and generation of lithium dendrites can be effectively suppressed by improvement of the interface stability. Therefore, improvement of the capacity retention ability of a battery is facilitated.