The effects of vanadium microalloying on the hardness and its distribution of alloy ZG270-500 smelted in intermediate frequency induction furnace were studied. Vanadium microalloying increased the hardness of test alloys effectively. By scanning electron microscope (SEM) and energy disperse spectroscope (EDS) analysis, it was found that VC was the powerful heterogeneous nuclei, which prompted numerous nucleating, refined the structure grains and caused the serious crystallographic lattice distortion, so the hardness increased. Proper content of vanadium prompted more even hardness distribution across the whole temperature front section. However, overdoes vanadium microalloying easily caused mass oxides of V2O3, which kept solid phases with high meting point in metal liquid to increase the viscosity and decrease the fluidity of metal liquid, resulting in inadequate metal liquid feeding, serious structure shrinkage porosity in center and worse hardness distribution along the different isotherm fields. 0.16wt.% vanadium microalloying brought the optimal hardness uniformity among test alloys with the approximate 1 hardness ratio R between the center and the margin.