As promising high-temperature structural materials, refractory high-entropy alloys have widely applications due to their excellent mechanical properties, high-temperature stability and oxidation resistance. For further improving the mechanical properties, ceramic-reinforced refractory high-entropy alloy matrix composites were prepared by utilizing in-situ reaction sintering. The supersaturated body centered cubic (BCC) solid solution of Cr_0.5MoNbWTi doped with nonmetallic elements of carbon, nitrogen and oxygen was prepared by mechanical alloying. During spark plasma sintering, (Nb,Ti)(N,C) and Ti₂O₃ ceramic reinforcements were formed by in-situ reaction between nonmetallic and metallic elements. The ceramic reinforcements were well dispersed in BCC matrix. The formation mechanism and the strengthening effects of the ceramic reinforcements were discussed in this paper. With the assistance of the fine-grained ceramic reinforcements, the composites exhibited ultra-high ambient-temperature strength (4033 MPa), ambient-temperature hardness (11.57 GPa), and superior high-temperature yield strength (572 MPa at 1400 ℃).