Abstract: The fluid flow phenomena in the bath of a rectangular tundish are studied in a water model, based on the dimensionless Fr and Re similarity criteria. The velocity vectors distribution diagrams are measured with LDA under two work conditions, which one is a bath with dam and weir and another is dam-free. The momentum source of flow motion in the bath of tundish is the downward stream. The velocity of liquid stream is recorded by a high speed camera. The stream injects the surrounding liquid and forms a liquid-liquid jet with spread angle 10°~12°. The jet strikes the bottom of the tundish and then becomes the spread out flow. The dam can cut off the bottom flow and converts the flow route. The residence time distribution curves of the flow in two tundishes with different work conditions are measured. The flow distances are changed, so the separation efficiency of particles from liquid is also changed owing to arrangement of different dams and weirs. A higher dam or two dams are more effective for delay the bottom flow. The optimum arrangement of dam and weir is discussed.