Abstract: The objective of the research was to investigate effects of pretreatments of microwave, steam heating and adding sodium hydroxide on crystallinity and fiber structure of switchgrass. All treatments could decrease crystallinity of raw materials. Neutral detergent fiber, acid detergent fiber and lignin contents decreased when pretreatment of microwave and adding sodium hydroxide (NaOH) were used. Crude fat content also declined by adding sodium hydroxide. There was no difference on biogas production (28?486 and 28?686 mL) and the biogas production rate (453.60 and 456.79 mL/g) between untreated material and steam heated material. The anaerobic digestion decreased by adding sodium hydroxide because of high ratio of C/N, toxic effects of cationic and inhibitor. The results showed that all treatment could decrease contents of fiber of Panicum virgatum, but could not improve the anaerobic digestion.