A castor oil-based polyurethane acrylate（CO-PUA） was synthesized using castor oil，isophorone diisocyanate，and hydroxyethyl acrylate via a solvent-free method，and was used as photosensitive monomers. A series of UV-LED shadowless adhesives were prepared based on the mix of the as-prepared CO-PUA，reactive diluent，silane coupling agent，adhesion promoter，photoinitiator，and pentaerythritol tera（3-mercaptopropionate）（PETMP）. The effect of the amount of PETMP on the performance of the shadowless adhesiveswas investigated. The results showed that the UV-LED curable shadowless adhesives withPETMP exhibited the characteristics of thiol-ene“click chemistry”，which eliminated the harm of oxygen inhibition and shadowless adhesive was cured completely. Especially，when 0. 5 g PETMP was introduced，the tensile shear strength of the samples using PMMA-PMMA， PMMA-stainless steel，and glass-stainless steel as the bonding substrate reached 2. 44 MPa，5. 06 MPa and 5. 70 MPa，respectively.