Abstract: Carbon/Carbon (C/C) composites are key materials in the defense and aerospace fields. However, achieving low density while maintaining excellent macroscopic properties is currently a challenge. In this study, the microstructure of C/C composites was optimized by introducing graphene (GN) and regulate the heat treatment process (2400℃, 2700 ℃ and 3000 ℃) to reduce porosity, promote texture improvement and optimize the residual thermal stress. Therefore, GN-C/C composites with excellent compressive performance, thermal conductivity and electromagnetic protection performance at low density were successfully prepared. The results show that the density of GN-C/C composites treated at 2400°C is only 1.81 g/cm³, the Z direction compressive strength reaches 331.34 MPa, the thermal conductivity in the XY directions at room temperature was 71.25 W·m-1·K-1 and the electromagnetic shielding effectiveness reaches 44 dB. Compared with the C/C composites without GN modification, they have increased by 6.08%, 20.58%, and 41.94% respectively, and the porosity has decreased by 24%. This method based on nano-reinforcement and process synergy provides a feasible strategy for preparing high-performance C/C composites.