In order to improve the gas barrier properties of PET films, the intercalated sericite was used as a barrier material in the functional silicone resin coatings. Firstly, the functional silicone resin with excellent thermal properties and high crosslinking degree was prepared. Secondly, lamellar sericite was intercalated and characterized by SEM and XRD. It was found that the lamellar spacing changed to 1.053 nm, and the compatibility in silicone resin was improved. Finally, the water vapor permeability (WVTR) and the oxygen permeability (OTR) of the modified PET film were tested. The results showed that WVTR and OTR of the modified PET film reached 12.40 g/(m2·24 h) and 29.91 cm3/(m2·24 h·0.1 MPa) respectively, which indicated that the silicone resin modified by intercalated sericite successfully prevents the direct penetration of gas molecules, thus forming a "loop" when gas enters, prolonging its permeation path and effectively realizing high gas barrier performance.