To bond untreated polyethylene terephthalate (PET) substrate, a novel UV-/moisture-curable silicone-modified poly(urethane-acrylate) (SiPUA) oligomer was synthesized from isophorone diisocyanate (IPDI), hydroxypropyl silicone oil, 2-hydroxyethyl methacrylate (HEMA), and other additives, and the structure of synthesized oligomer was characterized by Fourier transform infrared (FTIR). Adhesive formulas were developed using the synthesized oligomer, N,N-dimethylacrylamide (DMAA), tetrahydro furfuryl alcohol (THFA) and active amine acted as reactive diluents; 1-hydroxy-cyclohexylphenyl-ketone (C-184) and benzophenone (BP) acted as photoinitiators; dehydrating agent, defoamer, flow agent and nanometer inorganic filler acted as additives. The compositions that can be cured by exposure to ultraviolet and also has capability of curing by exposure to moisture at room temperature showed high adhesion to PET substrate. Furthermore, to obtain higher bonding strength to PET substrate, optimal content of curing agent was researched. It was found that appropriate addition of curing agent to the UV-/moisture-curing formula contributed to a remarkable enhancement in adhesion strength, and the shear strength bonding PET substrate can reach 7 MPa in accordance with ASTM D1002. The degree of wetting and fracture surfaces of the bonded joints were analyzed by means of contact angle measurements, scanning electron microscope (SEM), respectively. Mechanic performance tests including lap shear strength, peel strength, adhesion, and hardness were also carried out.