The invention discloses a method for preparing a high-temperature-resistant oxidation coating on the surface of a carbon/carbon composite material. The method is implemented through the technical scheme that by means of the plasma surface activating technology and the double glow plasma surface metallurgical technology, the surface of an activated carbon/carbon composite material workpiece is etched through hydrogen plasmas; then, a nickel target serves as a source electrode, and a nickel-based infiltrated layer is prepared on the surface of the workpiece; a chromium target serves as a source electrode to prepare a nickel-chromium composite depositing coating; finally, siloxane is used as a precursor, oxygen serves as reaction gas, and a chromium oxide and silicon oxide compound coating is prepared on the surface of the workpiece. The bonding strength of the coating prepared through the method and a base body is high, components of the coating are distributed in a gradient mode, and high-temperature-resistant oxidation performance of the carbon/carbon composite material can be improved. The coating is prepared in one device, the technology is simple, and cost is low.