Abstract: According to the similarity theory, a physical model of molten iron ladle was established at a ratio of 1∶5 between the model and the prototype size, which was used for solid-liquid two-phase flow experiments to study the influence of the insertion depth and speed of the stirring blade on the particle dispersion behavior inside the molten iron ladle. On this basis, the volume of fluid (VOF) model and discrete phase model (DPM) in Fluent software were used to simulate and analyze the influence of blade size on the flow field of hot metal ladle and the dispersion effect of desulfurizer. The results show that when the insertion depth of the impeller is 95–125 mm, with the increase of the insertion depth, the number of particles at the bottom of the ladle increases first and then decreases, and the particle dispersion effect is better in the insertion depth range of 105–115 mm. When the rotational speed is 112–180 r/min, with the increase of rotational speed, the number of particles at the bottom of the ladle increases significantly and then decreases slightly. When the rotational speed is greater than 180 r/min, the number of particles at the bottom is basically not affected by the rotational speed. The physical simulation conditions with better particle mixing effect are the insertion depth of the impeller 115 mm and the rotational speed 147 r/min.There is a weak flow zone below the rotating blade, with a flow velocity below 0.4 m•s⁻¹. With the increase of the blade diameter, the overall velocity of the molten iron increases, the depth of the vortex deepens, and the range of the weak flow zone decreases. When the blade diameter exceeds 1 440 mm, the weak flow zone remains basically unchanged. At the same time, with the increase of blade diameter, the content of desulfurizer in the bottom area of hot metal ladle increases, which is beneficial to improve the utilization rate of desulfurizer and save cost. When the blade diameter is 1 540 mm, the central part of the upper surface of the impeller is exposed, indicating that excessive blade diameter is prone to entrain air and reduce the yield of iron. The blade is close to the wall of the molten iron ladle, which can increase the erosion effect of the fluid on the wall of the molten iron ladle and damage the working life of the molten iron ladle. According to the comprehensive stirring effect and the dispersion degree of desulfurizer, the particle mixing and desulfurization agent dispersion effect are better when the impeller diameter is 1 440 mm, and the optimal diameter ratio between the stirring blade and the molten iron ladle is 0.401.