Abstract: To investigate the effects of acid-alkali combination and ultrasound pretreatment on ethanol production from corncobs, the composition, crystallinity and saccharification rate of corncobs pretreated by Acid-Prior-to-Ultrasound Strengthened Alkali were tested by component analysis, GC-MS analysis, measurement of reduced sugar concentration, XRD and calculation of Jade. The results indicated that the amounts of both hemicellulose and lignin were reduced to about 14% by acid-prior-to-alkali pretreatment, and the amount of lignin was further reduced to 7.86% when strengthened by ultrasound with a power of 120 W for 5min in the alkali phase. Meanwhile, the saccharification rate was enhanced from 34.09% to 37.32%, and the crystallinity was reduced from 59.79% to 57.46%. These results suggest that the acid-prior-to-ultrasound strengthened alkali method may be employed in corncob pretreatment for ethanol production.