Ocean Thermal Energy Conversion (OTEC), a part of ocean energy, is a method for generating electricity by using working fluids to rotate turbines and by utilizing the temperature difference between surface seawater and deep seawater. This technology is currently on demonstration status with a scale of 1 ㎿. Regarding the experiences of the 1 ㎿ scale OTEC trial, a significant amount of pump power is necessary to supply sufficient seawater for the OTEC which leads to a decline in net power. To improve this situation, a model test of 1 ㎿ scale OTEC’s surface seawater flow line was constructed to decrease the head required from seawater intake to the top height of seawater pipeline by the siphon effect. Modeling of this module was done regarding the law of similarity, test environment, and supplementary components (valves, etc.) in order to facilitate the siphon effect. Flow characteristics were observed with and without the siphon mode operation and the electricity costs of the two modes was compared. As a result, 37.5% of the pump power was replaced by the siphon effect on the seawater pipeline model test of OTEC.