Biomass pretreatment is still a major challenge for improving bioethanol production. The performance of two alkaline-mechanical pretreatments, alkaline twin-screw extrusion (ATSE) pretreatment where both alkaline treatment and refining occur simultaneously and alkaline pretreatment followed by PFI refining (APR), was compared in pretreating corn stover for fermentable sugar production at the same pretreatment conditions: 99 degrees C for 1 h with alkali to biomass ratio of 0.06 g NaOH/g oven-dry corn stover and a 1: 2 biomass-to-liquid ratio. The enzymatic hydrolysis efficiency of glucan and total sugar yield of ATSE-treated samples was 87.47% and 78.75% compared to 64.80% and 54.83% of APR-treated samples (alkaline pretreatment with the supplement of 10000 revolutions refining) with a cellulase loading of 20 FPU/g for 48 h. X-ray diffractometer (XRD), and scanning electron microscopy (SEM) explained why ATSE pretreatment obtained the satisfied total sugar yield with low temperature and high biomass/liquid ratio and also demonstrated ATSE pretreatment was an effective method for improving enzymatic hydrolysis rate of corn stover.