The invention discloses a preparation method of in-bag fermented pickled radishes, and belongs to the field of biological technologies and food. The invention aims to solve the problems that the production cost for preparation of the fermented pickled radishes at present is high, salt and acid are high, the waste water drainage amount is large, the color and flavor are unstable, fermentation is not controllable, large-scale standard production is difficult to realize and the like. Steps of raw material pretreatment, sterilizing and cleaning, dewatering, blending, vacuum bagging, fermentation and the like are controlled, particularly, ready-to-use lactobacillus powder and primary metabolites thereof are added and various parameters and indexes in a preparation process are controlled, the problem that gas produced from mass propagation of special-shaped fermentation microorganisms goes bad can be avoided effectively, the color, flavor, brittleness and plumpness of the in-bag fermented pickled radishes in expiration date after the fermented pickled radishes are bagged are maintained, waste water is not generated, after fermentation is finished, the pickled radishes can be directly sold, secondary processing is not required, and thus, clean and standard processing of the fermented pickled radishes is realized.