Supercritical carbon dioxide (scCO2) combined with an ultrasound method using 15–25MPa and the temperature range of 120–170 C for 0.5–4h was proposed as a pretreatment for corn cob and corn stalk with moisture contents of 50%. The results showed that both scCO2 pretreatment and scCO2 combined with ultrasound pretreatment could improve the total reducing sugar yields of the two materials. Enzymatic hydrolysis of both corn cob and corn stalk sugar using scCO2 pretreatment was increased by 50% and 29.8% compared with the control samples, respectively, while they were increased by 75% and 13.4%, respectively， using the scCO2 combined with ultrasound pretreatment under our experimental conditions. Following treatment from the two pretreatment processes, X-ray diffraction results indicated no significant change in crystallinity of the two materials. However, scanning electron microscopy images demonstrated that the microscopic structure of lignocellulose changed considerably and the surface area of lignocellulose increased significantly.