Abstract: The influence of high temperature aging at 950 ℃ on the microstructure evolution and high temperature mechanical properties of 20Cr32Ni1Nb steel were studied by optical microscope, field emission scanning electron microscope,high temperature tensile, high temperature impact, hardness analysis, etc. The results show that a large amount of secondary carbides precipitate in the substrate during the long-term aging process. The growth and coarsening of NbC and M23C6carbides occur on the branches and grain boundaries, and NbC transforms to G phase. Compared with the properties of the original state, the yield limit and tensile strength of the material increase slightly at the beginning of aging, and then decrease continuously. At the same time, the change of extension shows a monotonous downward trend. The impact toughness at high temperature decreases greatly with the increase of aging time, and then increases slightly. After long-term aging, the impact toughness at high temperature shows a continuous and slow downward trend. During the whole aging process, the hardness first increases slightly and then decreases monotonously. In general, the decrease of the hardness is limited.