Abstract: WC-Co cemented carbides are widely used in cutting tools and wear-resistant components owing to their high hardness and excellent wear resistance. However, their mechanical properties are jointly governed by several factors, including WC grain size, sintering process, and preparation method. To regulate the microstructure and improve the overall mechanical performance of WC-Co cemented carbides, WC-Co-based cemented carbides were prepared in this study from WO₃, Co, and carbon black by spark plasma sintering (SPS) combined with the in situ carbothermal reduction of WO₃. Graphene was introduced as a reinforcing phase, and the effects of graphene content and sintering temperature on the phase composition, microstructure, and mechanical properties were investigated. The results show that SPS promotes the in situ reduction and carburization of WO₃ to form WC as the main phase. An appropriate amount of graphene helps regulate the local carbon potential and suppress abnormal growth of WC grains. When the graphene content was 0.4wt.% and the sintering temperature was 1400 ℃, the specimen exhibited a relatively dense and uniform microstructure, an average WC grain size of 0.64 μm, and relatively good continuity of the Co binder phase. The Vickers hardness reached 2131.1 HV, and the indentation fracture toughness was 12.8 MPa·m^1/2, and the parabolic oxidation rate constant K_p was 0.4111×10⁻⁶ g²·cm⁻⁴·s⁻¹. Under these conditions, the specimen exhibited relatively favorable comprehensive properties. This study reveals the correspondence between graphene addition and microstructural evolution and property regulation WC-Co cemented carbides prepared by SPS-assisted in situ synthesis, and provides a reference for the design and fabrication of graphene-reinforced WC-Co cemented carbides.