WC-Co based ultrafine cemented carbide has become an ideal material for manufacturing high-performance metal cutting tools due to its excellent comprehensive mechanical properties. In order to improve the comprehensive properties of WC-Co based cemented carbides, ultra-fine cemented carbide with different contents of vanadium carbide (VC) were prepared, and the effects of VC addition on the (V, W)C cubic phase agglomeration and its morphology evolution as well as mechanical properties of three-dimensional WC grain during sintering process were systematically studied. Additionally, thermodynamic calculations were utilized for theoretical analysis of the agglomerative of (V, W)C cubic phase. The results showed that the solid solubility of VC reached saturation and agglomerative (V, W)C cubic phase occurred in the microstructure when the addition of VC was up to 0.6%. Further increasing VC content, the size of agglomerated structure significantly increased, which greatly affected the uniformity of the material. The segregation of VC at the WC/Co interface results in WC grains exhibiting a stepped triangular prism morphology. The stepped three-dimensional morphology becomes more pronounced with increasing VC content and sintering temperature. As the VC content increases from 0.1% to 0.6%, the coercivity of the cemented carbide significantly increases, and the Vickers hardness also shows an upward trend, while the fracture toughness decreases. When the VC content reaches 0.6%, the cemented carbide exhibits optimal comprehensive performance, with Vickers hardness and fracture toughness of 17.9 kN/mm2 and 8.9 MPa·m1/2, respectively, and the relative magnetic saturation and coercivity are 88.5% and 31.57 kA/m, respectively.