In this study, numerical simulations are conducted for the inundations due to storm surge and rainfall at Masan City of Korea where severe damages occurred by the typhoon Maemi. A coupled numerical model which can deal with various flow patterns such as storm surge, rainfall and sewer flows is employed. The numerical results show that the inundation area and depth increase significantly when the combined effects of storm surge and rainfall are considered in comparison with those obtained without a rainfall effect. Further numerical simulations are conducted to evaluate the performance of the sea wall being constructed for the coastal defence. The results show that the maximum inundation depths decrease when the sea wall is constructed. However, the duration of inundation becomes longer, because the rainwater on the ground cannot be discharged easily to the sea due to the presence of the sea wall.