The construction of continuous thermally conductive networks within polymers typically requires high loadings of thermally conductive fillers. Reducing the filler loading threshold while minimizing the detrimental impact on the mechanical properties of the matrix remains a significant challenge in developing thermally conductive polymer composites. To address warpage deformation during the melt cooling and solidification of polycarbonate ( PC) and enhance its mechanical performance, this study employed chopped carbon fibers (CFs) as reinforcing fillers and spherical alumina (Al₂O₃) particles as thermally conductive fillers. Leveraging the complementary synergistic effects between fillers of different dimensions and morphologies, a dualfunctional network for both thermal conduction and reinforcement was successfully constructed at reduced overall filler content. This approach achieved simultaneous improvements in the mechanical properties, thermal conductivity, and heat resistance of the modified polycarbonate. The study focused on the influence of the size and loading content of chopped carbon fibers and spherical alumina on the structure and properties of the modified PC composites. Results demonstrate that the incorporation of CFs and Al₂O₃ significantly enhance the mechanical properties, heat deflection temperature (HDT), and thermal conductivity of PC, while also markedly reducing its coefficient of thermal expansion (CTE). With the addition of 20% CFs and 20% spherical Al₂O₃(5 μm), the composite achieves a tensile strength of 131.6 MPa, a elastic modulus of 15.4 GPa, an HDT of 141.1 ℃, and a thermal conductivity of 0.59 W/ (m·K). When the alumina mass fraction is increased to 50% , the CTE values decrease significantly to 7.8 × 10^-6 ℃^-1, 25.6 × 10^-6 ℃^-1, and 45.9 × 10^-6 ℃^-1 in the X, Y, and Z directions, respectively.