In this work, novel WC-(Ti,Ta,Mo,V,Cr)(C,N)-Co (WC-HECN-Co) high-entropy composite powders were prepared by carbothermal reduction nitriding at 1400 °C and subsequently sintered by spark plasma sintering (SPS) to obtain cemented carbide. The preparation, microstructure and mechanical properties were investigated. The results show that, during the synthesis of WC-HECN-Co, phase evolution follows: (oxide raw material) → (WO3, CoWO4, WO2, V2O5, Ta2O5, Cr2O2.4, CoO, V6O11, TiMoO5, Co3W3C) → (W2C, Co3W3C, WC, WO3, Ta2O5, VO2, Ti6O11) → (WC, Co3W3C, TiTaC2, Ti6O11, Co) → (WC, Co3W3C, HECN, Co) → (WC, HECN, Co). The TEM elemental mapping results show that Ta, Ti, Mo, V and Cr are uniformly distributed with the WC grains to form a composite hard phase that is well bonded with Co. With the temperature increase, the Vickers hardness of SPS sintered WC-HECN-Co bulks gradually increased and the fracture toughness showed a trend of increasing and then decreasing. The Vickers hardness and fracture toughness of the WC-HECN-Co composite reached 1439 Kg·mm−2 and 12.19 MPa·m1/2, respectively. The fracture mechanism of sintered samples is jointly influenced by intergranular fracture and transgranular fracture. This study provides a novel strategy to develop high-performance cemented carbides that contain high-entropy carbonitrides.