Abstract: A model for fluid and heat transfer of early stage of filling of a 19 ton ingot mould was built, and the flow and tempera-ture distribution characteristics during early stage of filling were investigated. Numerical simulations of mould filling with a series of en-trance nozzles with the different top diameters and bottom diameters were carried out, and the effects of entrance nozzle structure on mould powder entrapment during early stage of filling were investigated. The results show that level fluctuation in molten steel is strong and solidified shell grows fast so that mould powder can be entrapped easily. When top-end interior diameter is larger than bottom-end, the velocity of molten steel stream depends on the bottom-end interior diameter, and decreases with the increasing of op-end interior di-ameter. As for 19 ton steel ingot, the risk of mould powder entrapment can be greatly decreased when the bottom-end interior diameter is larger than 90 mm.