The invention discloses yam bean dietary fiber powder with a prebiotic function and a preparation method thereof.The yam bean powder is prepared by taking fresh yam bean tuberous roots as raw materials through the steps of cleaning, peeling, slicing, color protecting, first-time grinding, freezing grinding, limited enzymolysis performing and drum drying, crosslinking adsorbing, complexing, secondary grinding, mixing, extrusion granulating, sieving and packaging, the prepared yam bean powder retains all dietary fibers of the yam beans and the original flavor of the yam beans, contains high-resistance starch and has the instant solubility and the prebiotic function.According to the yam bean dietary fiber powder with the prebiotic function and the preparation method thereof, embedding crosslinking, complexing, enzymatic debranching treating and drum drying are combined to be applied to the production process of the yam bean dietary fiber powder, the dissolving ability of the yam bean powder can be effectively improved, the fluidity and solubility are improved, the content of the resistance starch in the product is increased, and the significant effects on regulating the intestinal microecological balance and improving the gastrointestinal function are achieved; in addition, powder granules produced through extrusion granulating are uniform in granule size, loosened and porous and can be swelled and gelatinized in a short time, and therefore the good instant solubility and wet permeability are achieved.