Abstract: The wheat straw was pretreated by alkali ethanol solution to increase the total sugar conversion in enzymatic hydrolysis process,and characterize the change in lignin structure. Based on Box-Behnken design,temperature,mass fraction of alkali and time were chosen as the three important factors with three levels. The process conditions of alkali ethanol solution pretreatment were optimized by response surface methodology,and a second order quadratic equation was established,and the applicability of the model and interaction involved factors on predicting the yield o total sugar conversion was verified. The results indicated that the effects order of three factors on the total sugar conversion were as follows:Mass fraction of alkali,temperature and time. The optimal levels for achieving the highest total sugar conversion were obtained,including temperature of 140℃,mass fraction of alkali of 1.19% and reaction time of 2.37 h. The total sugar conversion reached 96.78% under optimized conditions(on the basis of original enzyme substrates). Chemical composition and scanning electron microscopy analysis showed that 84.62% of lignin was removed through alkali alcohol pretreatment(on the basis of original wheat straw). The compact structure of fiber was damaged,and the pores and cracks formed on the fibril promote the accessibility of substrate and enzyme,and increased the efficiency of enzymatic hydrolysis. The characterize of FT-IR showed that the most groups got better retention except part of the C=O bond and C-O-C bond ruptured. Lignin as a pretreatment byproduct had great potential application value.