Abstract: The effects and mechanisms of the pulling velocity and the nozzle immersed depth on the flow characteristics of liquid protective slag and molten steel have been analyzed by establishing a mathematical model of a three-dimensional continuous casting slab mold with multiphase flow of steel and slag. The results show that when the pulling velocity is increased from 1.0 m/min to 1.4 m/min, the slag flow velocity at the interface between steel and slag, the ideal central-surface of liquid slag, and the upper surface near the liquid slag are significantly increased, with an increase of 68.2%, 112.9%, and 68.6%, respectively. When the nozzle immerss depth increases from 140 mm to 240 mm, the flow rate of the protective slag on the above three surfaces shows a downward trend, decreasing by 7.3%, 19.6% and 12.2%, respectively. The change of pulling velocity has a greater impact on the flow behavior of the liquid protective slag than the change of the nozzle immersed depth. By optimizing the flow control of molten steel and protective slag, the flow behavior of the liquid protective slag of the mold can be effectively improved, which provides data support for the further optimization of the continuous casting mold process.