Liquid Eucommia ulmoides gum (LEUG) with different molecular weight were synthesized, and through the reaction between the amino groups of levodopa (LDOPA) and epoxy groups on the LEUG molecular chains, levodopa-grafted liquid Eucommia ulmoides gum (LEUG-g-LDOPA) was prepared by emulsion process. The bond strength and water- resistance of LEUG and LEUG-g-LDOPA as wood adhesive were investigated and compared with commercially water-based epoxy adhesives. The structure and properties of LEUG-g-LDOPA were analyzed by nuclear magnetic resonance hydrogen spectroscopy (¹H- NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and rotational viscosity meter. The adhesive properties of LEUG and LEUG- g- LDOPA to wood were investigated by lap shear test. The results show that with the increase of molecular weight, the lap shear strength of LEUG adhesive on wood increases and then decreases, and the maximum lap shear strength is 2.91 MPa at M_n = 1.51 × 10⁴ . The lap shear strength of LEUG-g-LDOPA is up to 5.74 MPa, which is 97% higher than that of LEUG, and the adhesive strength is comparable with that of water-based epoxy resin adhesive. In terms of water resistance, the wet lap shear strength of 1.99LEUG- g-LDOPA is 3.14 MPa, which is higher than that of LEUG and water- based epoxy resin. The strong adhesion of LEUG- g- LDOPA to the wood is related to the presence of the flexible chain structure of LEUG, polar groups on the main chain and catechol- structured LDOPA pendent groups. The good water- resistance mainly comes from the hydrophobicity of LEUG and strong chemical interaction between LEUG-g-LDOPA and wood surface.