Abstract: In order to solve the key technical bottleneck for fuel ethanol production regarding the removal of inhibitors during co-fermentation of hexose and pentose, four main non-lignin constituents of corn stover, including cellulose, hemicellulose, hot water extractives and ethanol extractives, were prepared and then treated with 0.75% dilute sulfuric acid at 180 ℃ for 40 min, respectively. 60 g/L glucose and 30 g/L xylose were added to these prehydrolyzates. 5 various ethanolic fermentation medium were fermented to produce ethanol by Candida shehatae, respectively. Thus, the influences on ethanolic co-fermentation and the origination of the key inhibitors were comparatively studied. The results showed that the degradation products formed from 133 g/L corn stover inhibited microbial glycometabolism and co-fermentation totally. During pretreatment of corn stover by dilute sulfuric acid products degraded from four non-lignin constituents reduce the ethanol yield at different extents. Additionally, the products released from the cellulose degradation can completely inhibit the xylose fermentation. Glucose and xylose could be completely inhibited by the degradation products from hemicellulose, and these products perform lethal toxicity to Candida shehatae as well. The products generated from hot water extractives and ethanol extractives exert inhibition on cell growth and sugars utilization. The key inhibitors were mainly from degradation reaction of cellulose and hemicellulose during the pretreatment of corn by stover dilute sulfuric acid. Besides formic acid, acetic acid, levulinic acid, HMF and furfural in corn stover prehydrolyzates, other unknown degradation products also presented toxicity or synergistic inhibition on ethanolic co-fermentation of hexose and pentose.