Abstract: This study adopted a high-alloy 02Cr20Ni18Mo5Mn6N austenitic stainless steel as the research object and systematically analyzed the precipitation behavior of secondary phases in the tested steel under different aging temperatures and aging durations. Thermo-Calc thermodynamic calculation, scanning electron microscopy, transmission electron microscopy and other experimental characterization methods were combined in the research to support the application research of composite pipes serving in harsh service environments. Thermodynamic calculation results show that the single-phase austenite region of the tested steel ranges from 1 080 ℃ to 1 330 ℃. Due to the high contents of Cr, Mo, Ni and N elements, the tested steel exhibits complex precipitation behavior in the temperature range of 700 ℃ to 1 080 ℃, where Cr₂N, Cr₂₃C₆, Laves phase and σ phase are precipitated. After solution treatment at 1 150 ℃ for 1 h, the alloying elements in the tested steel are fully dissolved. The microstructure consists of completely recrystallized and uniformly distributed equiaxed austenite grains with a large number of annealing twins. As the aging temperature increases from 700 ℃ to 1 100 ℃, the type, morphology and distribution of secondary phases in the tested steel change gradually. The Cr-rich σ phase at grain boundaries is coarsened gradually and transforms into Cr-Mo composite σ phase. In the grain interior, the single nanoscale Cr₂N evolves into multiple Mo-rich phases with diverse morphologies including Cr₂N, Cr₂₃C₆, the Laves phase and the σ/χ phase, and all precipitates finally dissolve back into the matrix at high temperatures. The temperature range of 800 ℃ to 900 ℃ is the sensitive temperature interval, where the tested steel presents the most complex precipitation behavior and the most abundant types of precipitates. According to the observation results of aging treatment at 900 ℃ with the duration varying from 10 min to 48 h, the precipitates preferentially nucleate and grow at grain boundaries, and then all precipitates at grain boundaries and grain interiors undergo rapid growth and coarsening comprehensively. The JMA kinetic model can accurately predict the precipitation behavior of the tested steel during the aging process.