The invention discloses a method for preparing seasoning instant osmunda japonica thumb. The method comprises the following steps of: S1, washing fresh osmunda japonica thumb, blanching, cooling to room temperature and salting; S2, elutriating the salted osmunda japonica thumb, draining water, adding white granulated sugar, filling in a fermenting tank, inoculating a complex microbial inoculant, and fermenting; and S3, removing part of salinity of the fermented osmunda japonica thumb, seasoning, vacuum packaging and bagging by adopting an aluminum foil compound pocket, and sterilizing. The method has the beneficial effects that alcoholic fermentation is carried out by utilizing acid-resisting yeast and taking sugar as a culture medium, obvious and faint soy sauce flavor is generated by virtue of common effects of saccharomycetes and lactic acid bacteria, thus unique taste and flavor of the instant osmunda japonica thumb are obtained, and the nutritive value of the instant osmunda japonica thumb is improved; the complex microbial inoculant can reduce the pH of the environment, inhibit growth of harmful microbes, and also has the capacity of degrading nitrite so as to guarantee the edible safety of the product; the fermentation period is greatly shortened, the yield is increased, and the agriculture efficiency and income of farmers are increased; and the method is simple, the technology is mature, the method is easy to popularize, and industrial production is realized.