Based on approximation principle, water model experiment was carried out during teeming in a 60t steel ladle. Based on the previous research work, trapezoidal nozzlein with lager upper cross section was used to decrease the critical level of vortex in order to reduce the slag entrapment to the tundish. Different shape and height of upper part of the nozzle was investigated mainly to inhibit the vortex at the late stage of ladle teeming. When upper shape of trapezoidal nozzle is square, upper height is 20mm and 17mm, and eccentricity of nozzle is 3/4, critical height of vortex is about 34mm and 31mm. In this case, slag entrapment is controlled effectively and metal utilization is optimized more completely.