To improve the performance and expand applications of poplar plantation wood, modified poplar veneers based on 1-butyl-3-methylchloride ([Bmim]Cl) were studied. Two groups of poplar veneers were impregnated in ionic liquid [Bmim]Cl (group C) and pure water (group B), separately. Techniques such as hot pressing-coagulation and bath-annealing were applied to these two groups to prepare modified samples. The physical and mechanical properties of each group were tested and characterized, using untreated group (A) as the control. The ductility and thickness variation rate of samples in group C were higher than those in group B. The width variation rate of samples in group C was 64% greater than those in group A and 50.4% greater than those in group B. Scanning electron microscopic (SEM) results also showed the plasticity and the improvement in the transverse connection of samples in group C; these results were more obvious than that for samples in group B. The tensile strength and elastic modulus of samples in group C were higher than those of group B. Compared with the control group, the crystallinity index (CrI) of samples in groups B and C was increased and that of group C was the maximum, but the crystal form remained unchanged.