The alkaline hydrogen peroxide (AHP) pretreatment (0.5 g H2O2/g corn stover, 30 degrees C, 24 h) removed 91.53% of the initial lignin and 55.77% of the initial hemicellulose in corn stover and afforded a considerable glucose yield (88.34%) through enzymatic hydrolysis. A combination of chemical and microstructural analyses was used to illustrate the mechanism of the effect of AHP pretreatment on enzymatic hydrolysis. During pretreatment, H2O2 derived radicals effectively spread into and destroyed the cell wall of various parts (vascular bundle sheath, xylem vessels, tracheid, phloem, and parenchyma) of corn stover to remove most of the lignin, acetyl group, and partial hemicellulose. They destroyed the compact structure of the cellulose-hemicellulose-lignin network, increased the cellulase-accessible pore volume by 6 times, doubled the area of exposed cellulose, and decreased the unproductive adsorption of enzymes onto lignin. Combining all the effects, AHP pretreatment effectively improved the cellulose accessibility to enhance the subsequent enzymatic hydrolysis efficiency.