The aim of this paper was to improve the hydrophobicity and mechanicalproperties of waterborne polyurethane and expand its application range. Firstly，the dispersion of hydrophobic modified nano SiO₂ with double bonds and long-chain alkaneswas successfullyprepared using tetraethyl orthosilicate（TEOS），silane coupling agents γ -methacryloyloxy-propyltrimethoxysilane（KH570） and hydrophobic modifier hexadecyl trimethoxysilane（HDTMS）. Then，the prepared dispersion was directly added to waterborne polyurethane（WPU） lotion containing siloxane on the branch chain to in-situ synthesize the nano SiO₂/polyurethane UV curable hydrophobic coatings. The effect of modified nano SiO₂ content on the performance of nano SiO₂/polyurethane composite coatings was studied. The results showed that when themass fraction of modified nano SiO₂ in the total composite coating was 25%，the water contact angle of the prepared coating film could reach 117. 4 °，the 24-hour water absorption rate was only 1. 1%，the thermal decomposition temperature was increased by 50 ℃，and it also indicated good mechanical properties.