Abstract: Taking 15Cr1Mo1V reheated steam pipeline running for about 1.3×10⁵h in a power plant as research object,the samples of repairing weld heat affected zone of shielded metal arc welding were prepared by welding thermal simulation test, and the peak temperatures of welding thermal cycle were 720 ℃, 820 ℃, 890 ℃ and 1300 ℃, respectively, which were corresponding to the tempering zone, incomplete phase transition zone, complete phase transition zone and coarse crystal zone of the joint. The microstructure, hardness, impact toughness were analyzed. The results show that the microstructure of the parent metal of 15Cr1Mo1V steel in service of 1.3×10⁵h is granular bainite+a little of polygonal ferrite, and there are granular carbides in the grain and grain boundary. After welding thermal cycle, the microstructure of the tempering zone is basically the same as that of base metal, the pearlite transformation occurs in incomplete phase transition zone, the microstructure of the complete phase transformation zone is pearlite+ferrite+grain boundary carbides, and that of the coarse grain zone is coarse lath bainite. The hardness of base metal, tempering zone and incomplete phase transition zone of 15Cr1Mo1V steel after 1.3×10⁵h of service is lower than the specified value in DL/T 438-2016, while the hardness of coarse grain zone is higher than the requirements. Service of 1.3×10⁵h has no obvious effect on the impact toughness of 15Cr1Mo1V steel. The impact toughness of tempering zone and coarse grain zone is higher than that of as-supplied base metal, but the toughness of incomplete phase transition zone and complete phase transition zone is significantly lower than that of as-supplied base metal.