Abstract: The residence time distribution(RTD) obtained from a pulse tracer experiment is always used for characterizing the flow fluid in tundishes. However,it is not suit to multi-strand or asymmetric tundishes because of negative volume or deviations calculated by the typical combined model using the RTD. In this paper,the accumulated residence time distribution(F curve) obtained from a step tracer experiment is applied to dead volume and plug volume calculations. This method is appropriate for single-strand tundishes and multi-strand tundishes. In this way,a 7-strand tundish in a steel plant is studied for optimizing its flow control devices.In the end,the dead volume decreases,and the distribution of molten steel among the strands tends to uniform,which benefits the slab quality and production process.