Abstract: The ionic liquid has strong stability and excellent solubility to cellulose. Although bagasse is abundant in cellulose, the dissolution of bagasse without any pretreatment in 1-butyl-3-methylimidazolium chloride is very hard. In this study, a pretreatment method was introduced with mass fraction of 3% nitric acid and 1.5%NaOH pretreatment to remove hemicellulose and lignin. After pretreatment, the content of cellulose was 93.53%, and dissolution time reduced 5.88 times compared with the one without pretreatment. Moreover, the composition and structure of pretreated bagasse cellulose were characterized by fourier transform infrared spectrophotometer and scanning electron microscope, and these changes on the effect of dissolution time was also analyzed.