The invention belongs to the technical field of material science, and particularly relates to a repairing composite layer of an amorphous/nanocrystalline cooling roller and a preparation method of the repairing composite layer. The composite layer consists of two layers, namely a copper-based alloy layer connected with base materials and a nickel-based alloy layer, wherein the copper-based alloy layer comprises the following components by weight percent: 7-9% of Ni, 8-12% of Sn, 5-15% of Co, 0.8-2% of Si and the balance being Cu; the nickel-based alloy layer comprises one of Ni-Co alloy, Ni-P alloy, Ni-Fe alloy and Ni-Cr alloy, and the weight content of Ni in alloy is 60-75%. The preparation method comprises the following steps of pretreating the surface of the cooling roller, electroplating the copper-based alloy layer and performing wide-strip cladding on the nickel-based alloy layer by a high-power laser. The prepared composite coating is uniform and compact, and excellent in wear resistance and heat resistance, and has the characteristics of high cladding efficiency and high energy absorptivity of the cooling roller to the laser beam.