The depolymerization of biomass carbohydrate polymers usually happened in homogeneous medium, just a few in heterogeneous solution. Herein, holocellulose from two Chinese herb residues Cortex albiziae (HRCA) and Heteropogon contortus (HRHC) was prepared and characterized. Deep eutectic solvent (DES) of choline chloride/p-coumaric acid collaborating with water was employed for the dissociation of those two holocelluloses and selectively dissolved hemicellulose into xylose with maximal yields of 81.50 % and 72.47 %, respectively. Most cellulose remained as the polymer state with a maximum solubility of 9.38 %. The synergistic action of DES and water was investigated to unveil the depolymerization mechanism and the roles of each component in depolymerizing procedure. It was water that released hemicellulose polymers and dissolved polymers to soluble short oligosaccharides, and DES rapidly cleaved the latter to xylose. Contrarily, DES broke cellulose to only soluble cello-oligosaccharides, but water exhibited the ability to hydrolyze cellulose to glucose.