<p>Recently, deep eutectic solvents (DESs) have attracted much attention for biomass pretreatment. This study explored the use of a ternary DES system to enhance the lignin removal during the pretreatment of biomass and improve the enzymolysis efficiency of residual biomass after pretreatment. It also investigated the possibility of co-production of furfural and xylo-oligosaccharides. A ternary DES system synthesized using lactic acid (LA), cationic surfactant cetyltrimethylammonium bromide (CTAB) and metal chloride CuCl₂ was successfully used to achieve highly efficient removal of lignin and xylan, and the enzymatic digestion efficiency of biomass was significantly elevated. The pretreatment parameters were optimized by response surface methodology, and the results showed that the LA: CTAB: CuCl₂ system exhibited excellent pretreatment performance, which was able to efficiently remove xylan and lignin from the reeds and increase the saccharification efficiency to 79.5%. The accessibility of cellulose was improved, and both lignin hydrophobicity and surface area declined, acquiring a high enzymolysis efficiency. In addition, abundant furfural (4.5&#xa0;g/L) and xylo-oligosaccharides (3.4&#xa0;g/L) were detected in the pretreatment solution. The combined severity factor (CSF) value with furfural and xylo-oligosaccharides formation were fitted by Gaussian modeling. Finally, a potential mechanism for the efficient pretreatment capacity of LA:CTAB:CuCl₂ was revealed. The pretreatment method developed by this research can efficiently achieve the co-production of reducing sugars, xylo-oligosaccharides and furfural, realizing the high-value utilization of biomass.</p> Graphical Abstract <p></p>