Abstract Aramid fiber has been commonly used in EPDM-based insulators to enhance ablative resistance as the char layer skeleton, due to its good flexibility and low thermal conductivity. However, its thermal stability restricts the improvement of ablative performance to meet the growing requirements of Solid Rocket Motors. In this work, hybrid fiber network was constructed in char layer via the combination of aramid fiber (AF) and carbon fiber (CF), due to high thermal stability of CF. The results showed that linear ablation rate displayed a valley-shaped change as the CF ratio increases, and best ablative performance was obtained at the 1:1 ratio with the linear ablation rate reduced to 0.0604 mm/s, which was 31% lower than that of the insulator filled with only AF. Furthermore, the ablation mechanism was studied based on the evolution of char layer structure and the formation of char layer with CF shielded at surface and AF consolidated inside could account for the synergetic effect on ablation resistance.