Abstract: The microstructure and mechanical properties of the Inconel 740H alloy seamless tube for the high-temperature components of 700℃ advanced ultra supercritical units are studied under different heat treatment temperatures and holding times. The results show that the longitudinal average grain size of the Inconel 740H alloy seamless tube continuously grows with the increase of heat treatment temperature and the holding time; the apparent activation energy of grain boundary migration in the alloy seamless tube within 10~60 min is 462.26~537.08 kJ/mol, which increases with the increase of time; the longitudinal average grain size of the seamless tube shows a parabolic relationship with the heat treatment holding time, and with the increase of temperature, the dynamic time index η increases first and then decreases; the tensile strength decreases with the increase of the heat treatment temperature and the holding time, and the effect of the heat treatment temperature on the tensile strength is greater than that of the holding time; the hardness of the seamless tube and the longitudinal average grain size conform to the Hall-Petch relationship.