Abstract: Influences of the carbide transition,carbide size and content in a failed 12Cr1MoV steel superheater on the material properties were studied by means of electrolytic extraction,XRD and EDS.The results show that the important reason of material property deterioration of the pearlite heat-resisting steel in the long-term high temperature service was due to the aggregation and growing up of carbides as well as transition of the carbide type.Analyses of carbides might provide a method to judge whether the 12Cr1MoV pearlite heat-resisting steel should be regarded as useless or not.This method was more reliable and practical than the analytical method of pearlite spheroidization.