Abstract: The austenite grain growth behavior of KT5331 steel and the effect of precipitates on the austenite grain growth were studied by isothermal austenization at 950-1280℃. The results show that the austenite grain growth process can be divided into three stages. Due to the pinning effect of precipitates containing W and Nb,the austenite grains grow slowly below 1075℃. Most of the precipitates dissolve above 1075℃,leading to the austenite grains coarsened. When the temperature rises to 1225℃,δ-ferrite precipitates and results in austenite grain refinement with increasing temperature. The austenite grain growth models below and above the coarsening temperature 1075℃ were established by numerical fitting.