In this study, low-cost dimethyldimethoxysilane was used as the main raw material to prepare and synthesize polydimethylsiloxane (PDMS) through hydrolysis condensation reaction, and then it was introduced into castor oil-based waterborne polyurethane (CWPU-SOP) to prepare modified castor oil-based waterborne polyurethane (PDMS/CWPU-SOP) with antifouling performance. The results showed that when the amount of PDMS was 8%, the contact angle of PDMS/CWPU-SOP film was increased by 25? to 110?, and the water absorption of PDMS/CWPU-SOP film was decreased by 7% to 15%. PDMS improved the film's hydrophobicity and water resistance. PDMS/CWPU-SOP film can roll freely on the surface of different acid and alkaline droplet without leaving any trace, with a certain antifouling performance.