In this study, the sloshing phenomenon is analyzed for the internal fluid mass change. And the change of the sloshing modeling design variables according to the fluid mass change is also analyzed. First, the sloshing phenomenon for each case is analyzed by CFD when the internal fluid mass is fixed. An appropriate sloshing modeling structure is proposed based on the analyzed results. The PSO method, which is one of the parameter optimization methods, is used as a method for appropriately selecting design variables of proposed sloshing modeling. In the same way, assuming a situation where the internal fluid mass changes in several levels, the sloshing modeling design variables for each internal fluid mass are calculated. The internal fluid varies from 10% to 90% in 10% increments so it is divided into 9 levels. By understanding the relationship between the optimized modeling design variables and the internal fluid mass, a sloshing model can be proposed to respond to the internal fluid mass change. (C) 2018 The Authors. Published by Elsevier B.V.