The invention discloses a preparation method of a silicon carbide surface oxidation film. The method comprises the following steps that 1) a silicon carbide material (10) including a substrate (11) and an epitaxial film (12) is cleaned; 2) nitrogen plasma processing is carried out on the upper surface of the epitaxial film (12); 3) a sample (13) obtained in the step 2) is preprocessed by argon at high temperature; and 4) a sample (14) obtained in the step 3) is oxidized to obtain the oxidation film (15). Passivation is carried out on the surface of silicon carbide before that the silicon carbide oxidation film is formed, the quality of the silicon carbide oxidation film is improved, the interface state density of silicon carbide/silica is reduced, and the method is easy to carry out, and suitable for large-scale industrial production.