Abstract: The effects of nitrogen on microstructure and properties of the austenitic hot die steel adding 0.208wt% nitrogen were studied by microstructure observation, mechanical and hot stability properties tests. The results show that the major precipitation phases in the tested steel was V(C, N)after adding nitrogen, and the hardness of nitrogenous steel increased by 2 HRC, its hot stability at 750 ℃ was better, and its hardness value was above 45 HRC within aging time of 20 h. The room temperature transverse impact energy of nitrogenous steel decreased by 8%, because the vanadium carbonitride being on grain boundaries to decreased grain boundaries strength.