The chemical composition, surface hardness, fracture morphology and microstructure of the fracture failure part for H13 steel mold insert were detected and analyzed by direct reading spectrometer, digital Rockwell hardness tester, optical microscope, scanning electron microscope and energy dispersive spectrometer. The results show that the failure of mold insert is caused by the severe overheating in the forging process resulting in the extremely coarse grain of the structure, which significantly reduces the material strength. However, the intergranular melting holes of lowmelting point inclusions in the matrix structure further reduce the strength and toughness of material, and the such as carbides and sulfides and precipitate phases brittle along the coarse grain boundary which reduce material strength and increase intergranular brittleness. Simultaneously, tempering at the grain boundaries is not sufficient, and the tissue stress increases significantly to produce intergranular crack. Thus, the lowstrength and highbrittle mold insert are difficult to withstand the external stress eventually resulting in tapping rupture in fitting process.