Paecilomyces thermophila J18 was a novel fungus isolated from soil and preserved in our lab. This strain produced a high-level extracellular β-xylosidase utilizing corncob as carbon source and urea as nitrogen source in the liquid-state fermentation. The result of single-factor-experiment revealed that 5% corncob of particle size 0.45mm～0.9mm, 1% urea, initial pH 6.5 and cultivation temperature of 45℃ were the optimal conditions for β-xylosidase production. β-xylosidase activity and specific activity were 3.15U/mL and 2.43U/mg respectively, after 5 days of cultivation in the optimized conditions. The birchwood xylan were degraded into xylose completely as the result of the synergistic action of xylanase and xylosidase from Paecilomyces thermophila J18, and the combination of xylanase and xylosidase enhance the reducing sugar yield by 64% comparing the xylanase single action after 24 h hydrolysis.