A new model was developed to analyze the coagulation behavior of inclusions in the molten steel during the secondary refining process. The advantage of the model is to calculate the behavior of two types of inclusions, such as alumina inclusion and slag-origin inclusion, which is a slag particle engulfed by the flow at the surface of the molten steel. The flow of the molten steel in a ladle is calculated by using a large eddy simulation model, and several kinds of inclusion collision modes are considered in the coagulation model. Inclusion analysis experiments were carried out in the secondary refining process, changing the flow rate of Ar gas injected from bottom of the ladle; the results were compared with the calculation. It is concluded that the increase in Ar gas flow rate increases the number of inclusions by enhancing the slag particle engulfed at the surface of the molten steel. The effect of Ar gas flow rate on the number of inclusions seems to be small within the range of Ar gas flow rate investigated.