Abstract: The low thermal conductivity of carbon fiber-reinforced high-performance thermoplastic resin matrix composites limited their application in heat dissipation. In this paper, carbon nanotubes (CNTs)@carbon fibers (CF)/poly(phthalazinone ether sulfone ketone) (PPBESK) composites were prepared by a combination of solution impregnation method and hot pressing. The thermal conductivity and mechanical properties were determined by thermal conductivity tester and universal testing machine, the fracture morphology of the composites was characterized by optical microscope and scanning electron microscope, and the T_g and energy storage modulus of the composites were determined by dynamic mechanical analysis. The results show that the introduction of CNTs formed a thermal conductivity network in the composites, and the thermal conductivity of the composites is increased to 1.016 W/(m·K), which is 72% higher than that of the pure CF-reinforced composites. Meanwhile, the mechanical properties of the composites are also significantly improved, and the flexural strength (1695 MPa), compressive strength (1001MPa),shear strength (70 MPa) and tensile strength of the CNTs@CF/PPBESK composites were increased by 28,37,14 and 17%, respectively, compared with those of the pure CF/PPBESK composites. The T_g and energy storage modulus of the modified composites are also determined to be improved.