The invention discloses a method of preparing a high-temperature oxidation-resistant coating on the surface of a refractory metal material. The method is characterized in that by adopting a plasma arc spray welding technology, a Mo-Si-B alloy high-temperature oxidation-resistant coating is prepared on the surface of refractory metal. With the adoption of Mo-Si-B alloy powder containing required components, and by controlling a dilution rate, coating components can be controlled, and a foundation is established for the flexible design of the coating components; compared with the traditional pack cementation method, thermal spraying method and magnetron sputtering method, with the adoption of the plasma arc spray welding technology, the coating bonding strength, the coating thickness and the coating compactness are improved obviously, and a guarantee is provided for the Mo-Si-B alloy high-temperature oxidation-resistant coating which is long in service life. According to the Mo-Si-B alloy high-temperature oxidation-resistant coating, the oxidation resistance at high temperature of refractory metal like molybdenum, niobium, tantalum and alloys of molybdenum, niobium and tantalum is improved effectively, and the service lives of refractory metal spare parts are prolonged obviously.