Corn stalk was treated by steam explosion, and the structure of untreated/treated corn stalk were detected by Scanning Electron Microscope (SEM) and X-ray diffraction(XRD), while their chemical composition were also investigated. Comparing with the untreated corn stalk, reducing sugar yield of treated corn stalk was increased by 197% after hydrolyzing for 24h. The relative content of hemicelluloses and solvend decreased, while cellulose increased by 29.7%; the compact structure of corn stalk was remarkably destroyed. The optimum steam exploded process condition: operating pressure 2.2MPa, solid-liquid ratio 1:1, reaction time 9min and materials size 40-60 meshes.