This work tailored a promising two-step pretreatment, i.e., liquid hot water extraction followed by mild acidic deep eutectic solvents pretreatment for clean lignocellulose fractionation while enhancing cellulose reactivity for its subsequent utilization. The abilities of three acidic deep eutectic solvents (formic acid-, acetic acid- and lactic acid-choline chloride) to selectively extract poplar wood lignin and enhance cellulose reactivity were comparatively assessed. Results showed that rather high lignin selectivity of 6.3-7.9 was obtained while the available area and porosity of the resulting cellulose were significantly increased. The resulting cellulose pulps exhibited comparable chemical reactivity to commercial bleached Kraft pulp when cellulose acetate was selected as testing cellulose derivative for demonstrating purpose, showing their great promise for high-value use. It was proposed that the unique ionic properties of these acidic deep eutectic solvents were responsible for their selective lignin removal and cellulose swelling/deconstruction to enhance cellulose chemical reactivity.