The effects of titanium modification, which was added along with the pouring liquid in ladles, on the hardness and its distribution of cast steel ZG45 smelted in intermediate frequency induction furnace were studied. Titanium modification increased the hardness of cast steel effectively. By scanning electron microscope (SEM) and energy disperse spectroscope (EDS) analysis, it was found that TiC, acting as heterogeneous nuclei, could refine the structure grains, causing the serious crystallographic lattice distortion. So the hardness increased. Proper content of titanium prompted more even hardness distribution across the whole temperature front section. However, overdoes titanium modification easily caused mass nitrides or oxides, which kept solid phases with high meting point in metal liquid to cause difficulties in metal liquid filling and shrinkage, resulting in less concentrated shrinkage cavity and serious structure rarefaction. The hardness ratio between that of internal and external with overdose titanium modification decreased instead compared to that of none modification.