Abstract: In order to improve biodegradability of perennial grass, batch mesophilic anaerobic digestion to produce biogas were conducted using material of King grass from southern China. Modified Gompertz equation was used to fit the cumulative biogas production. The results showed that the crystallinity of raw materials decreased, which decreased from 4.73 to 3.29 when the pretreatment by steam heating. Biogas yield was significantly increased after steam heating pretreatment, and the biogas production rate of 581.05 mL/g VS was achieved, about 63% higher than that of the untreated material. Lag phase were 1.7, 1.8 and 0.5 d after preteratment, the lag phase was significantly reduced compared to raw materials without pretreatment (5.9 d). The pretreatment methods can significantly improve the anaerobic digestion performance of perennial King grass.