Abstract: Reduced diameter monopile, as an emerging type of supporting structure for offshore wind turbines, it is very significant for engineering applications to calculate the sinking resistance of this stage. The laboratory scale test is difficult to truly restore the sinking characteristics, and the prototype test is time-consuming and labor-intensive. The Coupled Eulerian-Lagrangian（CEL） numerical analysis method can realize the static sedimentation process simulation of the original scale foundation. Based on the experiment results, the CEL numerical method is validated and applied to a simulation of an engineering prototype. The numerical simulation results show that the reduced diameter design increases the pile sinking resistance, and the EVF cloud image shows that the volume of soil entering the pile decreases, resulting in the reduction of the mud surface inside the pile. Finally, the influence of different sizes of reduced diameter monopiles on pile sinking resistance is studied.