Abstract: In the current work, observation was performed on the microstructure of different regions on the welded joint of a 2.25Cr-1Mo steel pipe that had been operating at 571 ℃ for about 260 000 h in a power plant. The creep damge in heat affected zone(HAZ) was mainly analyzed. The results show that the HAZ of welded joint intrades was mainly fine-grained structure. The creep cavity area in fine-grained zone was about 0.8% when steel pipe approached the design life, which could be a criterion for the creep failure of welded joints made of the same material. There were many MnS inclusions inside the fine-grained zone accompanied by cavities and microcracks, which was a factor of affecting the creep life of the welded joint.