In order to improve the production of reducing sugar yield from corn stalk by water/ ethanol extraction after steam explosion, the enzymatic hydrolysis process was optimized. With the response surface methodology, the production of reducing sugar yield can reach 672.36mg/g, when the substrate concentration of 53.8g/L, cellulase loading of 53.32FPU/g and reaction time of 60.45h. Compare to untreated and steam exploded corn stalks, the production of reducing sugar yield increased by 179.21% and 37.29%. Chemical compositions of untreated/treated corn stalk were investigated and their structures were also detected by Scanning Electron Microscope (SEM) and X-ray diffraction (XRD). The results showed that: the relative content of cellulose in corn stalk treated by water/ ethanol extraction increased significantly, the relative crystallinity increased, but the changes of structure lead to the cellulase attach on easier.