Abstract: The hydrodynamic response of side-by-side mooring system between the spent fuel carrier and the marine nuclear power platform（MNPP） is a complex engineering problem. This paper predicted the motion responses of the marine nuclear power platform when the spent fuel carrier is in side-by-side operation based on the three-dimensional potential theory. The “false resonance” problem in the calculation process is solved by adding lid damping term. And then,the impact on hydrodynamic performance caused by the spacing of two ships is studied, which can be of help for the side-by-side mooring system engineering design.