The invention provides a urea-phenol-formaldehyde resin cross-linking agent. The cross-linking agent is obtained through the following steps: reacting formaldehyde with phenol under the action of an alkali catalyst, adding urea and carrying out a reaction, wherein a molar ratio of the formaldehyde to the phenol is (3-4):1, a ratio of the total mole of phenol and formaldehyde to the mole of the urea is (4-5):1, and the catalyst accounts for 0.2-0.5% of the sum of the masses of formaldehyde, phenol and urea. Phenol formaldehyde resin is modified with urea to synthesize the urea-phenol-formaldehyde resin cross-linking agent, so the amount of reactive groups in the phenol-formaldehyde cross-linking agent is reduced, curing of urea-phenol-formaldehyde resin is prevented, and the stability of the urea-phenol-formaldehyde resin is improved; and the phenol-formaldehyde resin is modified with the urea, excess urea consumes excess formaldehyde, and no formaldehyde is released during storage, transportation and use, so environmental protection requirements are met.