The effects of steam explosion (2.5 MPa, 200s) and Trichoderma koningii (T. koningii) fermentation on corn straw degradation were evaluated according to straw degradation and enzyme activity in the fermented products. The results showed that the steam explosion pre-treatment for corn straw could reduce the contents of cellose, hemicellulose and lignin by 8.47%, 50.45% and 36.65%, respectively (P<0.05). After the pretreated corn straw with steam explosion was fermented by T. koningii for 6 days, the contents of cellulose and hemicellulose in the fermented straw were decreased by 19.37% and 63.54%, compared with the original corn straw (P<0.05); decreased by 11.83% and 26.41%, compared with the exploded straw (P<0.05). The filter paper cellulase, CMCase and amylase protease protease protease;activities in the fermented products were 356.39,5 599.90 and 834.00 U/g, respectively. It is concluded that the corn straw pre-treated by steam explosion and followed by T. koningii fermentation for 6 days seems to be a new prospective method for corn straw degradation and application.