Abstract: The flow field of four-strand tundish of round billet under three different weirs has been studied by water model experiments.The results show that a big difference in fluid flow characteristics exists between the two outlets at the same side of the tundish controlled by the original weir.Compared with the inside outlet, the outside outlet has longer minimum residence time and peak concentration time and larger dead zone volume.So the original weir can not meet the technical requirements for inclusion floatation and temperature homogenization.U-shape weir can satisfactorily settle the flow synchronism between outlets, but has short minimum residence time and large dead zone volume.Y-shape weir is the optimal shape of the three, which can change the fluid flow of the tundish efficiently and improve inclusion removal and raise steel cleanliness.The industrial test shows that Y-shape weir is better than the original one in reducing total oxygen and inclusions of billets.