The invention provides a preparation method of a 
soybean sprout powder, wherein the method includes the steps: (1) under 
germination conditions, making soybean germinated; (2) crushing and pulping the obtained soybean sprouts, at the temperature of 40-45 DEG C, carrying out enzymolysis treatment for 2-3 hours, hydrolyzing soybean isoflavone 
glycoside contained in the soybean sprouts into soybean isoflavone aglycones; (3) adding a 
mixed solution of 
ethanol and 
ethyl acetate into the pulp obtained in the step (2), centrifuging to obtain an upper solution and 
soybean sprout dregs; and (4) removing the upper solution, carrying out 
vacuum drying on the obtained 
soybean sprout dregs and crushing, and thus obtaining the soybean sprout 
powder. According to the method provided by the invention, through removing the soybean isoflavone aglycones, gamma-
aminobutyric acid with more content can be produced in the soybean sprout 
powder ultimately, the defect that conventional soybean sprouts and products thereof have the application range (especially application in the infants and children eating field) limited due to containing of soybean 
isoflavones as phytoestrogen is overcome, and thus the soybean sprout powder becomes a possible in the field of infants and young children foods.