High-entropy transition metal carbides (HETMCs) have emerged as promising candidate materials in advanced structural application due to their superior physical and chemical properties compared to traditional carbides. Among these materials, (TiVNbMoW)C has garnered attention due to its outstanding mechanical properties and wear resistance. However, previous studies on the single-phase formation process of (TiVNbMoW)C and the effect of carbon vacancy concentration on its mechanical properties remain inadequate. In this study, TiC, VC, NbC, Mo₂C, WC, elemental W powder, and graphite powder were innovatively selected as raw materials, and (TiVNbMoW)C_x with different carbon vacancy concentrations was successfully prepared by spark plasma hot pressing sintering technology. Effects of carbon vacancies on phase composition, phase evolution, microstructure, and mechanical property of the material were systematically studied. The results show that in the Ti-V-Nb-Mo-W-C system, the carbides corresponding to Mo, Ti, Nb and V elements began to dissolve into each other at 1500 ℃, forming (MoTiNbV)C phase. With increase of temperature, W element gradually participates in solid solution, resulting in densification of the material at 1700 ℃, and formation of (TiVNbMoW)C as a high entropy single phase occurs at 1800 ℃. The mass ratio of carbon to transition metals (C/TM) has a great influence on phase structure and microstructure of the material. When the C/TM is 0.7, the W element cannot dissolve sufficiently to form a single-phase structure, resulting in a composition consisting of (MoTiNbV)C and W₂C phases. At a C/TM of 0.8, the sample exhibits a single-phase (TiVNbMoW)C structure characterized by a large number of carbon vacancies. At a C/TM of 0.9, carbon vacancies reach saturation. At a C/TM of 1.0, excessive carbon enrichment within the material results in a decreased degree of densification. An optimal concentration of carbon vacancies is beneficial for grain refinement and enhancement of the mechanical properties of materials. The sintered sample with a C/TM of 0.8 exhibits the highest hardness, elastic modulus and fracture toughness, demonstrating the most favorable integral mechanical properties. Therefore, this study provides an important basis for a comprehensive understanding of (TiVNbMoW)C_x high-entropy carbides. Future research may introduce additional elements to optimize material properties and broaden its application in high-end manufacturing and related fields.