Abstract: A 3D steady numerical model of 1650 mm×220 mm slab mould was built,which was used to simulate the molten steel flow in the mould for with 3 schemes. The results showed that the width of the mould played an important role on the mould surface velocity. The velocity distribution became more and more non-uniform with the width increasing. The surface maximum velocity was affected by many factors,including the molten steel velocity at nozzle,nozzle angle,and the immersion depth of the nozzle,of which the molten steel velocity at nozzle had the most influence. The optimum scheme is as follows:mould width of 1100 mm,immersion depth of 120 mm,construction bottom structure of "E-lie-down" shape,nozzle outlet angle of 30°,flow rate of 11.6 m³·h^-1,and inlet velocity of 0.8384 m·s^-1.