Abstract: Orthogonal experiments of control device arrangement in different slab casting tundishes were carried out to study the influence of the reactor's structure on the flow characteristic of molten steel. The optimal arrangement rule of control devices and its effect on the flow characteristic of molten steel and inclusion removal were mainly analyzed. A quantificational relation of control devices, dead volume and the structure factor D was determined. The results indicate that the steel cleanness can be reflected by dead volume while the piston flow volume is disadvantageous to inclusion removal. There is a great influence of outlet pumping action on the fluid flow pattern, so the best distance between the dam and outlet is 1000 to 1300 mm, which results in the decrease of nozzle blocking rate to 7.5%. The relation between the flow characteristic of molten steel and the dam's relative location is obtained at normal casting speed when 0.0035 < D < 0. 0055. As the relative speed of inclusions to molten steel reaches to 6 ×10^-5m·s^-1, the floating speed of inclusions becomes faster.