Abstract: In this work, the impacts of ChCl/carboxylic acids, molar ratios of hydrogen bond acceptors to donors, pretreatment temperature and time on the delignification of poplar were investigated. Characteristic methods including XRD, FT-IR, GPC, and HSQC were used to analyze the solid residue and extracted lignin for the study of the structural evolution of the three components. The results showed that under low temperature of 90 ℃, the delignification of poplar wood was 91% with ChCl/FA pretreatment. About 63% of lignin was collected and the purity of lignin was 90%. Over 98% cellulose remained intact with I_β type crystal form, and the crystallinity was 70%. The β−O−4 bond content of extracted lignin was 84.8% (71% of the original β−O−4 bond), and M_n of the lignin was 1400, suggesting the extracted lignin to be an ideal raw material for monophenlics production.