<p>C/C composites and Nb metal were brazed using AlCoCrFeNi_2.1 eutectic high-entropy alloy filler (EHEA), whose FCC + BCC structure synergistically enhanced brazed joint due to its excellent match between strength and ductility. The microstructure evolution and mechanical properties of the joint brazed under different temperature and holding time was evaluated. The typical joint could be divided four regions and corresponding phase composition was C/C + FCC/M₇C₃ + NbC + BCC/BCC + Laves + FCC/Nb(s,s) + Nb₇Ni₆/Nb. The soft FCC phase provided the plasticity storage for brazed joint while in situ generated Laves phase gave it distinctive high-temperature performance. Elevating the brazing temperature or extending the holding time, the penetration zone near the C/C side gradually enlarged, the reaction layer of M₇C₃, NbC and Nb₇Ni₆ became thicker, and eutectic structure was gradually consumed while Laves phase was relatively enriched. Moreover, the joint strength first increased and then decreased, and the optimal joint was obtained at 1300 ℃ for 10&#xa0;min, whose strength at room temperature (RT) was 25.6&#xa0;MPa and corresponding high-temperature strength was 14.9&#xa0;MPa at 800 ℃. The fracture mainly occurred the penetration zone inside the C/C composites, subsequently stretched into the thick and brittle NbC reaction layer with elevating brazing temperature.</p>