Secondary hardening ultra-high-strength steel is widely utilized in aerospace and other advanced engineering, with the nanoscale M₂C precipitates serving as the primary strengthening factor. Mo plays a crucial role in the forming of Mo₂C secondary hardening phase, which can form composite M₂C precipitates with elements such as Cr, V, and W, thereby modifying the composition and properties of Mo₂C. To investigate the effects of V and W doping on Mo₂C, first-principles calculations are used to analyze the formation enthalpy, electronic structure, and mechanical properties of the doped systems. The CASTEP module is utilized in this study, with the Perdew-Burke-Ernzerhof (PBE) functional adopted in the generalized gradient approximation (GGA) framework. The results indicate that V doping reduces the lattice parameters and the formation enthalpy, thereby enhancing structural stability. In contrast, W doping increases the lattice parameters and lowers the formation enthalpy but leads the structural stability to decrease. In terms of mechanical properties, V doping reduces toughness while increasing hardness, whereas W doping improves the strength-toughness balance by mitigating the rate of hardness reduction. Covalent bonds are formed within the system, with V and W doping changing their characteristics: compared with the C—Mo bond, the C—V bond exhibits weaker covalency, while the C—W bond displays stronger covalency. Additionally, V doping enhances the stability of Mo—C bonds, whereas W doping reduces their stability. Charge population analysis reveals that metal atoms (Mo, V, and W) act as electron donors, while carbon atoms act as electron acceptors.