Abstract: After 1050 ℃×1.5 h solid solution and-73 ℃×2 h cold treatment, 1Cr15Ni4Mo3N steel was aged at different temperatures for 3 h. The effects of aging temperature on the microstructure and mechanical properties of the test steel were studied by means of SEM, TEM, universal testing machine and impact testing machine. The results show that, after solution and cold treatment, the tensile strength, yield strength and elongation of the test steel after 460 ℃×3 h aging reach the peak, and the impact energy of the test steel after 580 ℃×3 h aging reaches the peak.The microstructure of the test steel after 460 ℃×3 h aging is lath martensite and retained austenite with high density dislocation. The characteristics of lath martensite of the test steel after 540 ℃×3 h aging is weakened, and the content of reversed austenite test steel after 620 ℃×3 h aging is increased obviously.