Abstract: Early failure occurred to a H13 hot working mould during service, and a failure crack was found on its working face. Metallographic microscopy (OM), Rockwell hardness testing (RHT), scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS) were used to analyze and compare the microstructure, matrix hardness and microelement distribution of the samples. By analyzing the experimental results, the conclusion can be drawn: the early failure of the H13 mould is fatigue fracture. The fracture was caused by uneven matrix microstructure, non-metallic inclusions and many harmful impurity elements. It is suggested to improve the metallurgical quality of the steel, improve the heat treatment process and strictly control the content of non-metallic inclusions and harmful elements to guarantee the high fatigue strength and long service life of the mould steel.