Multi-layer circuit board has the problem of poor heat dissipation performance, which limits its application in high frequency circuit. In this experiment, polytetrafluoroethylene (PTFE)/SiO₂ high thermal conductivity composite film materials were prepared with Al₂O₃ as filler to enhance the thermal conductivity of multi-layer circuit boards. PTFE/SiO₂ composite films were prepared by impregnation process combined with high temperature sintering by adding different amounts of Al₂O₃ into PTFE. The effects of Al₂O₃ content on the microstructure, density, thermal conductivity and mechanical properties of PTFE/SiO₂ composite films were studied. The results show that with the increase of Al₂O₃ content, the thermal conductivity of the composite film shows an upward trend, and the density and mechanical strength show a trend of increasing first and then decreasing. When the Al₂O₃ content is 4%, the PTFE/SiO₂ composite film (sample 3) has the least micro-defects, the highest density and mechanical strength, and has a reasonable thermal conductivity and electrical insulation. The density of sample 3 is 2.119 g/cm³, the mechanical strength is 17.3 MPa, the thermal conductivity is 0.98 W/(m·K), and the volume resistivity is 380.9 GΩ·m.