Global warming is becoming worse owing to carbon dioxide emissions around the world, and eco-friendly energy for reducing carbon dioxide emissions is gaining importance. Wind power plants are the most representative of the environmentally friendly energy power plants built in the ocean. The fatigue loading and long-term dynamic behavior of offshore soils are important considerations in the construction of structures such as wind turbines in the ocean as they are subject to long-term loads such as wind and wave loads. A design graph presents the short- and long-term behaviors of soil. Several laboratory tests are typically conducted to create design graphs. In this study, a cyclic simple shear test conducted at various confining pressures and relative densities is presented in design graphs. The authors analyzed the sensitivity of the relative density and the confining pressure, and proposed a drawing technique to easily create two-dimensional design graphs. The authors found that the effect of the relative density on the design failure curve was higher compared with that of the confining pressure. The elliptic equation graph achieved the best match to the design failure curve, and the design failure curve drawing technique was summarized in five stages. In addition, the normalized cyclic stress ratio graph to distinguish safety or failure was presented.