Abstract: In the study, steam-explosion, a novel pretreatment method of substrate, was firstly introduced in the two-phased digestion system. Ammonium bicarbonate was used as added nitrogen source to adjust C/N in the system. Under the same conditions, experiments using NPWS (non-pretreated wheat straw) were processed as the control. Results showed that pH value in the hydrolysis reactor using SEWS (Steam-exploded wheat straw) was lower and increased slowly to 7 in 25 days. In methanogenesis reactors using SEWS and NPWS, pH value was all around 7, which is most suitable to produce methane. In the digestion system using SEWS, the content of TS (Total solid) and VS (Volatile solid) decreased by 57.5% and by 62.1%, respectively, about twice as high as NWPS. The degradation rate of cellulose and semi-cellulose of SEWS were 63.0% and 67.4%, respectively, much higher than NPWS. The degradation rate of the lignin is similar and about 5%. The total biogas yield of SEWS was higher and increased faster than NWPS. The methane content of the biogas was similar and was 50% in the hydrolysis reactor and 70% in the methanogenesis reactor. The results showed that steam-explosion pretreatment could promote the degradation wheat straw and increased the biogas yield. It is an effective method of pretreatment.