For improving the yield of reducing sugars from corn stalk enzymatic hydrolysis，the steam explosion was selected as an activation method，ionic liquid [BMIM]Cl was used as a further treatment step, the influence of steam explosion pressure and time on the the yield of reducing sugars was evaluated. The results showed that after activating with a steam pressure of 2.6 MPa for 90 seconds treatment, the yield of reducing sugars from [BMIM]Cl treated corn stalk can increase by 84.03% compare to activated corn stalk and by 286.83% compare to untreated corn stalk. The relative content of cellulose in [BMIM]Cl treated corn stalk increased by 64.86%. X-ray diffraction analysis (XRD) and Scanning electronic microscopy (SEM) indicated that the structure of [BMIM]Cl treated corn stalk changed into amorphous. The changes of structure lead to the cellulase attach on easier. So it came to the conclusion that corn stalk treated by [BMIM]Cl and activated by steam explosion can enhancing the yield of reducing sugars significantly.