The invention discloses a high-purity and high-concentration aluminum-boron intermediate alloy and a preparation method thereof, and belongs to the field of aluminum intermediate alloy production. Themethod comprises the steps of adding industrial pure aluminum to an alloy furnace for heating till complete melting, heating, and uniformly adding potassium fluoroborate to the aluminum melt in the alloy furnace in batches; after heat preservation, discharging the surface salt liquid; homogenizing the melt by electromagnetic stirring from charging to casting, and finally casting. The B content ofthe aluminum-boron intermediate alloy product obtained by the method is as high as 9.0-11.0wt%, the content of impurity elements is low, the content of each of transition impurity elements such as Tiand V is less than or equal to 0.015wt%, and AlB12 in the product microstructure is uniformly distributed in the shape of granules having the largest size of less than or equal to 100 microns and theaverage size of less than 50 microns.