The present disclosure relates to a method for controlling thermoplasticity and toughness of a redox-modified plant fiber, comprising following steps: (1) pretreating a plant fiber; (2) obtaining an oxidation-modified plant fiber by adding an oxidant solution, then filtering, and washing; and obtaining the redox-modified plant fiber by adding a reductant solution, then filtering, and washing; and (3) fully mixing a plasticizer with the redox-modified plant fiber; the plasticizer being a hydroxyl plasticizer, an ionic liquid plasticizer, a deep eutectic solvent, an ester plasticizer, an amine plasticizer, a glycidyl plasticizer, or an inorganic salt plasticizer. The method according to the present disclosure can improve the toughness of the redox-modified plant fiber material, reduce the processing temperature of the plant fiber material, and broaden the processing window of the plant fiber material.