The thermodynamic properties of the Co-V-C and Co-V8C7 systems are of interest for superfine cemented carbide applications. The model parameters for the Gibbs energy of the individual phases have been evaluated using the CALPHAD method by combining the recently optimized phase diagram information of the V-C, Co-C and Co-V system. The isothermal sections of ternary system Co-V-C at 1400 °C and 1600 °C, as well as the vertical section of Co-V8C7 system were extrapolated. The calculated results, especially the liquid forming temperature of Co-V8C7 system was validated with experiments by using differential scanning calorimetry (DSC) analysis. Through controlling the carbon activity, various vertical sections with different carbon activity in Co-V8C7 system are presented.