Deep eutectic solvents (DESs) are considered one of the most promising biomass pretreatment reagents, and their research applications in woody fibrous biomass are increasing yearly. Inspired by the research related to wood bending, we explored the effects of different DES systems on the bending development of wood, and the results showed that the addition of anhydrous ferric trichloride to the DES system of lactic acid/choline chloride could enhance the treatment effect that increased the bendability and torsion resistance of ash wood. The anhydrous FeCl₃ could act as an active site and provide acidic protons to improve the treatment efficiency of DES. In addition, the addition of an appropriate amount of water can reduce the viscosity of the DES system, and the highest lignin removal rate was obtained at 10 wt% of water in the DES, which resulted in the best mechanical properties and tensile resilience of ash wood, with the tensile strength and stability of 97 MPa and 13.6%, respectively, as determined by experiments with different water contents in different mass fractions. Therefore, using a DES can effectively improve the bending properties of wood.