Natural convection will obviously influence the liquid steel flow in continuous casting (CC) tundish, which cannot be neglected in tundish metallurgical process. Through the theoretical analysis, the dimensionless number, Gr/Re 2, is adopted to determine the convection pattern in tundish system. Validity of this criteria in a reduced scale water model are also discussed in this paper. Non-isothermal water model experiment with the temperature variation of inlet stream, has been simulated to see the effect of temperature variation of ladle stream. The convection pattern of molten steel flow in continuous casting tundish is also studied numerically by using the commercialized computational fluid dynamic (CFD) software package, CFX4. From the results of theoretical analysis, physical and mathematical model simulation, it can be stated that the convection pattern of molten steel flow in tundish is controlled by the combined nature convection and forced convection.