A microwave plasma generating device for plasma oxidation of SiC, comprising an outer cavity and a plurality of micro-hole/micro-nano-structured double-coupling resonant cavities disposed in the outer cavity. Each resonant cavity includes a cylindrical cavity. A micro-hole array formed by a plurality of micro-holes is uniformly distributed on a peripheral wall of the cylindrical cavity, a diameter of each of the micro-holes is an odd multiple of wavelength, and an inner wall of the cylindrical cavity has a metal micro-nano structure, the metal micro-nano structure has a periodic dimension of λ/n, where λ is wavelength of an incident wave, and n is refractive index of material of the resonant cavity. The outer cavity is provided with an gas inlet for conveying an oxygen-containing gas into the outer cavity, and the oxygen-containing gas forms an oxygen plasma around the resonant cavities for oxidizing SiC; a stage is disposed under the resonant cavities.