The shipbuilding industry has been drastically affected by demand fluctuations. Currently, it faces intense global competition and a crisis because of an imbalance between supply and demand. This imbalance of supply and demand is caused by an excess of shipbuilding capacity. The Organisation for Economic Co operation and Development has considered adjusting the shipbuilding capacity to reduce the imbalance based on the demand forecast. On the other hand, demand forecast of shipbuilding is a complex issue because the demand is influenced indirectly by adjustments in shipbuilding capacity. Therefore, it is important to examine the influence of construction capacity adjustments on the future demand of ships based on demand forecasting for the sustainable growth of the shipbuilding industry. In this study, shipbuilding capacity adjustment is considered using a proposed simulation system based on a demand forecasting model. Additionally, the system dynamics model of a previous study is improved by developing a ship price prediction model for evaluating the shipbuilding capacity adjustment scenario. We conduct simulations using the proposed demand forecasting model and system to confirm the effectiveness of the proposed model and system. Furthermore, several shipbuilding capacity adjustment scenarios are discussed using the proposed system.