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In order to further evaluate the scientificity and availability of materials selection scheme of the advanced 700℃ ultra-supercritical (700 ℃ A-USC) thermal power units, regular sampling and testing were conducted on the candidate tubes operating on the 700℃ A-USC test bed of Huaneng Nanjing Power Plant. Three groups of Inconel 740H superheater tubes with different operation time (0 h, 10,000 h, 24,000 h) were sectioned and machined, and then their mechanical properties and microstructure characteristics were evaluated by means of OM, SEM, TEM. Results show that the R_p0.2 and R_m of Inconel 740H at room temperature (RT) and 700℃ decreased slowly with the extension of operation time. The impact absorbing energy at room and high temperature both decreased significantly from original aging state to operation for 10,000 h, but when the operation time further prolonged to 24,000 h, only slight decrease was observed. The microstructure evolution of Inconel 740H was mainly manifested in the increase of grain boundary carbide M23C6 and the coarsening of γ′ particles. In general, Inconel 740H boiler tubes exhibited good mechanical properties and microstructure stability during operation.