Abstract: In order to clarify the microstructure and property evolution mechanism of different sub-regions in10Cr9Mo1VNb steel welded joint during long term service, the bulk samples matched with the sub-regions in 10Cr9Mo1VNb steel welded joint after 50000 h service were prepared by different heat treatment processes and high temperature accelerated aging experiment, and the microstructures and hardness of both the thermal simulation bulk samples and the serviced welded joint were investigated by metallographic microscope, scanning electron microscope and digital microhardness tester. The results show that the bulk samples corresponding to the over-tempered zone, inter-critical zone, fine grain zone, coarse grain zone are successfully prepared by the following normalizing and tempering processes of 800 ℃/755 ℃, 850 ℃/755 ℃, 950 ℃/755 ℃ and 1300 ℃/755 ℃, respectively. Moreover, after accelerated aging at 650 ℃ for 200h, the hardness of these thermal simulated bulk samples is in good agreement with that of the sub-regions in 10Cr9Mo1VNb steel welded joint after service at 569 ℃ for 50000 h.