Total solids content(TS) and volatile solids content(VS) of banana stalk were tested, and the content of cellulose, hemicellulose and lignin. Pretreatment banana stalk by steam explosion with different pressures and different time of keeping pressure. Analysis of degradation law of banana stalk hemicellulose, cellulose and lignin content after pretreatment. The samples of the treated and untreated banana stalks were with drawn to determined cellulose, hemicelluloses and lignose contents in dry matter.The results showed that when the explosion pressure was 3.5MPa, the time of maintain steam explosion pressure was 4min, degradation rate of hemicellulose, cellulose and lignin was 67.29%, 18.99%, and55.40%, degradation rate of the overall content was 34.41%, These results indicate that pretreatment by steam explosion can degrade cellulose of banana stalks, and hemicellulose、 lignin were degraded significantly. The method of steam explosion are further advantages such as environmentally friendly and high-efficiency.