Abstract: Wheat Straw was pretreated by four kinds of pretreatment methods, namely, liquid hot water(LHW), soaking aqueous ammonia(SAA),sodium hydroxide(NaOH) and sodium hydroxide combined with ethanol(NaOH-ET). The effects of pretreatments on chemical composition and enzymatic hydrolysis were investigated. The results showed that LHW pretreatment resulted in the highest level of polypentose reduction. The removal rates of xylan and araban were 73.11% and 83.10% respectively at 188℃ for 40 min, but the delignification rate was only 21.32%. NaOH had a good capability in the removal of lignin and ash. The removal rates of lignin and ash were 72.00% and 75.93% respectively by 1% NaOH at 140℃ for 3 h. Because of the good solubility of lignin in the ethanol, the removal rate of the lignin pretreated by the combination of NaOH with 50% ethanol pretreatment was up to 84.11%. XRD results showed that the crystallization index of four pretreated wheat straw were greater than that of the raw material because of the removal of lignin and hemicellulose; the crystallization index of pretreated samples increased from 28.80% to 31.23%-33.61%. As lignin and hemicellulose were partly removed by pretreatment, the accessibility of cellulose and enzyme inereased. Under the conditions of cellulose enzyme 30 FPIU/g(of cellulose) and β-glucose glycosides enzyme 30 IU/g, enzymatic hydrolysis temperature 50℃, and reaction time 72 h, conversion ratio of total sugar increased obviously. Especially, total sugar conversion rate of NaOH-ET treated wheat straw reached 90.05%, which improved 7.5 times compared with that of raw material.