Abstract: Sanicro 25 austenitic heat-resistant steel was subjected to high-temperature aging treatment at 700 ℃on the basis of cold working.The effects of cold working and aging treatment on the microstructure, second phase precipitation and mechanical properties of Sanicro 25 steel were investigated.The results show that the size and shape of austenite grains in the cold worked Sanicro 25 steel tend to be homogeneous as the aging time increases; and there is continuous precipitation of M₂₃C₆ phase, which is transferred from grain boundary precipitation to intracrystalline precipitation, and the number is increasing. There are wrapped or flake shaped NbCrN phase precipitated in Sanicro 25 steel after different cold working and aging treatment. With the increase of cold working amount, the grain of Sanicro 25 steel becomes finer and twins appear inside the grain, and the hardness also tends to increase; the minimum creep rate of unaged Sanicro 25 steel decreases continuously and the creep performance increases continuously; while after 3000 h aging, the minimum creep rate increases continuously and the creep performance decreases gradually.