Nowadays, with electronics becoming more refined and integrated, the heat transfer problem between devices is becoming increasingly problematic, so thermal interface materials with good thermal conductivity are becoming more critical. In this paper, thermally conductive composites are prepared based on silicone rubber (SR), and boron nitride coated with tannic acid and grafted with hexamethyldisilazane (BN@TA-HMDS). After modification with TA-HMDS, BN@TA-HMDS and silicone rubber has excellent compatibility and can be well dispersed within the silicone rubber matrix. It can be found that when the mass part¹ of BN@TA-HMDS is 50, the thermal conductivity of the composites reaches 0.735 W/m·K, which is about 6 times that of pure SR. In addition, the viscosity of the composite before cured is significantly reduced. When the mass part of BN@TA-HMDS is 50, the system's viscosity is only 1/50 of the BN/SR at the same ratio. This work provides a good guideline for the mass filling to build a better thermal pathway to improve the material's thermal conductivity.