Although twin pipelines in series have been used to transport hydrocarbons in existing engineering practice, previous studies have mostly focused on the dynamic response of the seabed around a single pipeline. In this study, we adopted the two-way coupling algorithm of fluid-structure-seabed interaction to investigate the wave-induced soil response around twin pipelines with different pipe diameters. The present model integrated the wave model and the seabed response model in a two-way coupling algorithm by introducing a boundary condition of velocity continuity in addition to the continuity of pressures at seabed surface, which overcome the contradiction between physical phenomena and existing theoretical models. Numerical results demonstrated the difference between the present two-way coupling model and existing one-way coupling model.