Abstract: The investigation on the ageing of austenite hot work tool steel by internal friction shows that the height of the peak dumps and the width of the peak narrows after ageing at 720 °C×2 h and 550 °C×10 h, compared with before ageing. The result reveals that the carbon atoms which are solved in the austenite lattice are repartitioned during aging, and the content of the alloy in the austenite matrix phase reduces. By analyzing the kinetic age combining JMA equation shows that at the beginning of the low temperature aging, there is a planar flow of interstitial atoms from the austenite lattice to interface and defect, while during the high temperature aging process, the interstitials and the solved alloy atoms in austenite lattices form carbide and grow centered on the defects.