Abstract: The microstructure and mechanical properties of 12Cr1MoV steel pipe for the main steam pipeline of a power plant were studied by means of metallographic examination, mechanical property test and high temperature creep rupture test. The results show that after long-term high temperature service, the microstructure of 12Cr1MoV steel pipeline appearred 5 grade pearlite spheroidization, the precipitation of carbide in the crystal was obvious, the spheroidization degree and grain size grade of the inner wall, middle wall and outer wall of the steam pipeline were consistent, and the mechanical properties of the pipeline declined significantly. The remaining life of the pipeline was estimated to be about 4. 45 years.