Abstract: P92 steel had been widely used in high temperature components of ultra-supercritical units (such as steam piping and header) because of its excellent high-temperature comprehensive properties. However, there was still an urgent need to conduct research on the material degradation mechanisms and effective supervision methods to ensure the units' safe operation for long-term service. Microstructure analysis and mechanical property test of original P92 steel material for high temperature components of power plants were implemented. The evolution characteristics of material property and substructure had been traced for more than 10 years. The evolution law of microstructure and property was summarized and the degradation mechanism was studied. On this base, the relationship between material hardness, microstructure and degradation level was established for grade 92 steel during the whole lifetime, and a quick and nondestructive method for service supervision was proposed. Results show that the proposed method can provide a reference evidence for inspection, material evaluation and operational supervision of 9Cr steel in nuclear power plants.