The earlier failures are always occurred in the H13 steel continuous extrusion-wheel die for section copper and its alloy. The experimental analysis on the microstructures evolution of the extrusion-wheel die after different service times were made,and the tests showed that the martensite resolved into tempered martensite and the hardness reduced gradually in the surface layer of the groove of continuous extrusion-wheel die in the early stage service. As service time delayed,the martensite resolution accelerated and large quantities carbides precipitated,and the thermal fatigue cracking initiated from the subsurface of the groove. After that the services proceed,the martensite resolved completely and carbides coarsen seriously. The fatigue cracks of the subsurface layer drove towards the surface and propagated into the interior of the groove on the assistance of the melting copper alloy,which resulted in failure of the groove of the continuous extrusion-wheel die.