The invention relates to a preparation method of resistant dextrin. The method comprises steps as follows: (1) adding water to a raw starch material to adjust the concentration of slurry to obtain starch slurry; (2) adding high-temperature-resistant alpha-amylase to the starch slurry, and performing liquidation to obtain a liquidation liquid; (3) concentrating the liquidation liquid to obtain a concentrated liquid A, adding beta-amylase and pullulanase to the liquidation liquid obtained in Step (2), and performing concentration after the reaction to obtain a concentrated liquid B; (4) mixing the concentrated liquid A with the concentrated liquid B, and adding organic acid for reactions to obtain a reaction liquid; (5) decolorizing, filtering, ion-exchanging, concentrating and drying the reaction liquid to obtain the resistant dextrin. According to the method, the starch is used as the raw material, enzymes are combined for use, then the organic acid is added as a catalyst, and the resistant dextrin is prepared; compared with traditional preparation methods that the starch is directly used as the raw material and acids are added, the method is mild in reaction condition, few in side reaction, easy in refining and convenient to market.