Abstract: Mathematical and physical models of granulating process were established to elaborate the granulating mechanism of the gas quenching process of liquid steel slag,and flow fields of granulation process under different conditions were calculated through the FLUENT software.The simulation results show that N₂ jet flow can be divided into three phases,namely the initial phase,fundamental phase,and dissipation phase.The maximum velocity distributes on the axis of the jet flow,and the velocity is inversely proportional to radial distance.The impact kinetic energy and the flow field distribution of the N₂ jet flow have a significant influence on the effect of granulation.The ideal diameter of the Laval nozzle is 10 mm.The increase of mach number is helpful to enhance the impact kinetic energy of the jet flow,and thus contributes to the steel slag granulation.