Objective To synthesize a solvent-free polyurethane adhesive with high water resistance. Methods A series of polyurethane adhesives modified by polysilicone were synthesized using PBA, IPDI, castor oil and hydroxy silicone oil as materials. The chemical structure was characterized by FT-IR analysis and thermogravimetric analysis. Influences of different ratios of polysilcone on curing time, adhesion strength and water resistance were well discussed.Results The addition of proper amount of polysilicone could enhance the bonding strength, thermostability and water resistance. But overdose of polysilicone prolonged the reaction time of the pre-polymer. Conclusion The content of polysilicone should be controlled within 3%~4%.