In order to ensure the original support of a multi-point mooring Floating Production Storage and Offloading (FPSO) to achieve safe operation in the severe sea conditions of the South China Sea, an external turret mooring system is designed and the hull is optimized. Based on the three-dimensional potential flow theory, the hydrodynamic calculation model is established by Wadam software and the frequency domain hydrodynamic performance of FPSO under different ship type schemes is studied, and the preferred ship type is determined. Through the time domain coupled dynamic analysis method, the motion response of the FPSO under the action of wind, wave and current are studied, and the motion response and mooring line tension results before and after the optimization of the hull are compared. The calculation results show that reducing the stern frame angle and increasing the stempost angle can reduce the pitch and heave motion response of this type of FPSO in the South China Sea to certain extent and the mooring system meets the requirements of the classification society.