Abstract: In order to study the mechanism of diluted acid pretreatment on enhancing cellulose conversion during cellulase hydro-lysis process, microscopic structure and physical/chemical characteristics of corn stover before and after diluted acid pretreatment were investigated. The cellulose conversion ratio increased from 31.88% to 95.74% when the corn stover was pretreated by 1.875% acid solution as a 1:15 liquid ratio at 170℃ for 60min. The XRD analysis showed that the crystallinity of cellulose increased from 31.88% to 58.7% after acid pretreatment. But only slight change of cellulose crystalline was observed when the corn stover was treated to some level. The rough fiber surface with more holes was detected after dilute acid pretreatment. This was beneficial for the connection between cellulose and corn stover. The specific surface area significantly increased from 0.329m2/g to 2.878m2/g after dilute acid pretreatment. It was also beneficial for enzymatic hydrolysis of corn stover cellulose.