Abstract: This paper presented a method to produce two kinds of xylanases in different application. High activity Xylanases (54.4IU/mL)with CMCase (3.4IU/mL)could be produced by Trichoderma reesei strain with pretreated corn cob as the carbon source. Xylanases could be produced selectively with coarse xylan mixed with cellulose as the carbon source, by controlling culture conditions in fed_batch fermentation. The degree of selective production was related to carbon source concentration. High activity of xylanases (35.5IU/mL)and low activity of CMCase (0.2IU/mL),with a high ratio of both enzymes (177.5),could be obtained from 10g/L of carbon source.