It suggested that the degradation of HMF and furfural was negligible under studied pretreatment conditions. As for acetic acid, it is a main co-product, which is formed primarily by hydrolysis of acetyl groups of hemicelluloses (Palmqvist and Hahn-Hägerdal, 2000). The amount of acetic acid increased greatly with increasing the temperature and time while the chemical dose did not show an obvious effect. When magnesium bisulfate concentration achieved 3.51%, acetic acid concentration increased to 4.337 g/L. In addition, the analysis of soluble sugar showed that MBSP produced less xylose and glucose in pretreatment spent liquor than SPORL and DA pretreatment. It might be caused by a higher pH environment, compared with pH 1.2 in the DA pretreatment and 2.7 in the SPORL pretreatment (Shuai et al., 2010).