Abstract: Objective: A xylanase B (CsXyn11B) gene from Chaetomium sp. CQ31 was extracellularly expressed to improve the enzyme production and explore its application in bread baking. Methods: The xylanase (CsXyn11B) gene was expressed in Pichia pastoris, and the enzyme production was improved by high-density fermentation. The enzymae was characterized and applied in bread baking. Results: The recombinant strain was fermented at high density for 156 h, and the enzyme activity of xylanase was 2788 U/mL. The optimal pH of CsXyn11B was pH8.0, and the optimal temperature was 65 ℃. CsXyn11B hydrolyzed a variety of xylans, and the specific enzymatic activities of oat xylan, wheat arabinoxylan, beech xylan and birch xylan were 1145.8, 1041.7, 692.3 and 653.3 U/mg, respectively. The enzyme hydrolyzed arabinoxylan, and the hydrolyzed product were mainly xylo-oligosaccharides with a degree of polymerization of 4~6. Addition of CsXyn11B (3 mg/kg) into the bread making remarkably improved the specific volume by 15.9% and decreased the hardness by 25.3%. Compared with the control group, the hardness decreased by 17% after storage at 4 ℃ for 2 d. Conclusion: The excellent properties of xylanase B from Chaetomium sp. made it have a promising application prospect in baked food.