Furfural (FF) is one of the most important platform molecules in the conversion of xylose and hemicellulose. However, the conversions of xylose and hemicellulose to FF with Brønsted acid (B-acid) and Lewis acid (L-acid) as catalysts suffer from harsh reaction conditions and low yield, respectively. B-L acid deep eutectic solvents (B-L ADESs), which consist of both B-acid and L-acid, were designed to catalyze the reaction of xylose and hemicellulose to FF under mild conditions. Surprisingly, B-L ADES exhibits excellent catalytic activity for the preparation of FF from xylose and hemicellulose, which exceeds most results reported thus far. Furthermore, it is proved from the kinetics perspective and density functional theory (DFT) calculations that the synergistic action of B-L acids has lower activation energy and higher FF yield than that of B-acid and L-acid alone. The strategy of B-L acid combination provides a theoretical basis for the subsequent design of sustainable catalysts.