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[Display omitted] • DES improved cellulase activity by mainly rising βG activity with 20–35% increase. • DES improved cellulase stability by compacting the spatial structure. • DES formed a protective layer to prevent unproductive adsorption of lignin on cellulase. • DES significantly increased the saccharification efficiency of corn stover and poplar. The introduction of specific choline chloride (ChCl)- and betaine (Bet)-based deep eutectic solvents (DESs) into the conventional acetic acid–sodium acetate solution led to a significant increase in cellulase activity and stability. In particular, a higher enhancement in β-glucosidase activity was obtained, which plays a key role in improving cellulase function. The DESs prolonged the half-life of cellulase. The addition of 10 % (v/v) ChCl/1,3-propanediol (1:2) and 5 % (v/v) Bet/glycerol (1:2) resulted in the most significant improvement, with the half-life of cellulase reaching three times the initial half-life value. The above both DESs allowed the cellulase to maintain an excellent level of activity over time, even after 72 h. The DESs tightened the structure of the enzyme by changing its secondary structure, which had a stabilizing effect on the overall conformation. The density functional theory calculations of DESs revealed that the DES with a more stable structure more effectively protected the active conformation. The molecular dynamics simulation on β-glucosidase indicated that the hydrogen bond donor end of the DES primarily formed hydrogen bonds with the enzyme, which induced a spatially compact conformation by increasing the α-helix content while reducing the β-sheet content. It also restricted the movement of amino acids, particularly stabilizing the active site, and increased the hydrophilic region, thereby enhancing enzyme activity and stability. In addition, the DES formed a protective layer that prevented the unproductive adsorption of lignin on the enzymes during the hydrolysis of lignocellulosic feedstocks. These multiple improvements provided by DESs significantly increased the enzymatic saccharification efficiency of corn stover and poplar. [ABSTRACT FROM AUTHOR]