Some cofferdam systems have been applied for marine structures construction of bridges piers, marine foundation, and etc. Recently, new cofferdam system using large scale of cylindrical members has been proposed to reduce marine working time and to improve economic. In this study, hydrodynamic behaviors of large steel-cylindrical cofferdam system were investigated analytically. Also, design shear force at the module-module connection part was evaluated. Based on the hydrodynamic behaviors, advanced cross-section of large steel-cylindrical cofferdam system was proposed so as to efficiently resist to hydrodynamic shear force and possible to reduce total weight of large steel-cylindrical cofferdam system.