Considering the whole process optimization of biogas production, low concentration of FeCl2 solution was studied as a catalyst for corn stalk pretreatment and hydrolysis liquid was inspected for anaerobic acidification fermentation. Optimum pretreatment conditions were found where the corn stalk was pretreated with 1 mg/L FeCl2 at 200 degrees C for 20 min. Through comparative study with distilled water in the anaerobic fermentation stage, the result showed that FeCl2 could speed up anaerobic acidification digesting process. The study provided a novel idea to evaluate the role of iron in the whole process from pretreatment to fermentation.