Abstract: The oxidation of styrene to benzaldehyde has advantages of mild conditions and no chlorine impurities in the product, and the design of highly active catalyst is the core. As a solid acid catalyst, WO₃ has excellent performance in thermal oxidation reaction, but its activity is limited by small specific surface area and high B acid content. In this work, the Cr^{3 +} cation was introduced as a modifier during the preparation of WO₃. The adsorption of Cr^{3 +} cations on non-(001) crystal plane realized the transformation of WO₃ from nanorods to ultrafine nanowires (UNWs), and the specific surface area of obtained Cr-WO₃ UNWs increased to 297 m²/g. In addition, Cr^{3 +} cation could dope into the lattice of WO₃ and slow down its crystallization, both of which effectively enriched the surface oxygen vacancies (L acid sites) of WO₃. In the reaction of selective oxidation of styrene to benzaldehyde, Cr-WO₃ UNWs effectively increased the conversion of styrene and the selectivity of benzaldehyde from 19.0% and 49.6% of pure WO₃ nanorod to 72.0% and 84.6% respectively under the optimized condition of 70 ℃, r(n_H2O2/n_styrene)=2.0, 6 h and m=30 mg. The improvement of catalytic performance can be attributed to the following two reasons:(1) the large specific surface area can provide sufficient active site for reaction; (2) the L acid site can activate H₂O₂ into active W-OOH, and an increase in the concentration of L acid site is beneficial for the production of more active species.