Abstract: In order to ensure the safety and reliability of multi-body floating operation system at sea, we present the retardation function approach based on the three-dimensional (3D) potential flow theory. The mathematical model of the coupled motion responses of multi-body floating operation system is established. The effect of hydrodynamic interaction of multi-body floating system is fully taken into account, and the motion responses of multi-body floating system are tested comprehensively under different wave headings. The motion performance of transport ship in close proximity to spar platform is investigated for offshore installation operation under different wave headings. Then the numerical simulation results are presented and compared with the model test results. Satisfactory agreements are achieved, proving the validity of the mathematical model. From the results, it is found that the local wave may generate an amplification or shadowing effect for multi-body system in close proximity offshore operation.