The study investigated the effects of two-step pretreatment on fermentable sugar production from corn stalk silage. In the first step, the corn stalk silage was extracted by tepid water and then the solid was pretreated using Fe(NO(3))(3) as catalyst. The results showed that 45.8 g/100g DM total sugars was obtained and the surface of remaining solid was seriously damaged after two-step pretreatment. Compared with one-step pretreatment, the production of total sugars increased by 23.8% and the amount of the catalyst of Fe(NO(3))(3) decreased by 28.8%. This research provides a new effective, suitable and economical pretreatment method for biogas production from corn stalk.