Abstract: The inclusion removal rate in molten steel is influenced by molten steel flow and the bubble/inclusion size. As the research results shown, the upward movement of molten steel is in favor of the inclusion floatation, and almost all of the inclusions can float up. Inclusion and bubble flotation is hindered by the downward molten steel flow. Bubbles whose diameters are smaller than 1 mm can not float up when the molten steel flows downward. In the ladle refining process, small gas injection rate should be used to avoid forming excessive big bubbles, which will reduce the gas-injection efficiency, and to reduce the molten steel velocities, which is good for the bubble/inclusion flotation. But the gas injection rate also should not be too small, which ensures that bubbles in molten steel maintain a certain size to fully float up. In the ladle refining process, both the molten steel velocity and the bubble size should be considered when choosing the gas injection rate.