The catalytic conversion of glucose to high value-added platform chemical 5-hydroxymethylfurfural (HMF) is a promising biorefinery process, and alumina-boria catalysts are considered to be green and mild solid acid catalysts for this catalytic reaction. Here, compared to the common synthesis methods with complicated steps, we reported a simple and efficient strategy to prepare B₂O₃-Al₂O₃ nanocomposites by calcining cost-effective glucose-urea deep eutectic solvent (DES) solution containing the precursors. The prepared B₂O₃-Al₂O₃ nanocomposites exhibited an open three-dimensional skeleton and two-dimensional porous lamellar substructure, endowing them with a high specific surface area (228.27 m²/g). The introduction of boron changed the ratios of different aluminum species (Al^Ⅳ, Al^Ⅴ, Al^Ⅵ) and borate species (BO₃, BO₄), thus further affecting the acidity and the types of acid sites of the materials. The prepared B₂O₃-Al₂O₃ bifunctional acid catalysts possessing abundant Lewis acid sites and adjustable Brønsted acid sites showed complete glucose conversion and 55.38% of HMF yield under the optimum conditions. Our study proposed a concise method to synthesize alumina-boria solid acid catalysts assisted by glucose-urea DES. We hope to extend the application and prospect of this efficient and simple synthesis strategy.