Abstract: The failure of the hot extrusion die of the valve stem is analyzed and a steel-hard alloy is adopted on trial as a substitute of the die material. The field experiment indicates that the steel-hard alloy used as hot extrusion die material has a wide application foreground, the life of the steel-hard alloy die is about 10 times of that of the predecessor die. The SEM observation shows that thermal fatigue is the major cause of the failure of the steel hard alloy die.