The　seismic　response　of　long-period　structures　such　as　isolated　buildings　under　the　far-field　long-period　ground　motion　is　strong,　and　the　response　may　be　even　greater　when　the　soil-structure　interaction　(SSI　effect)　of　soft　soil　foundation　is　considered.　Meanwhile,　the　torsional　effect　of　eccentrically　base-isolated　structures　under　two-way　horizontal　earthquake　action　may　lead　to　an　increase　of　displacement　of　isolation　layer.　To　study　the　influence　of　SSI　effect　of　soft　soil　foundation　on　the　seismic　response　and　damping　effect　of　eccentric　base-isolated　structure　under　the　action　of　far-field　long-period　ground　motion,　the　two-way　shaking　table　tests　on　a　scaled　model　of　a　4-story　eccentric　steel　structure　with　a　height　width　ratio　of　3　located　on　rigid　or　soft　soil　foundation　were　carried　out.　The　results　show　that　the　period　prolongation　ratio　of　the　structure　on　soft　soil　foundation　after　adopting　isolated　technology　is　lower　than　that　of　the　structure　system　on　rigid　foundation,　and　the　damping　effect　is　reduced.　SSI　effect　can　reduce　the　inter-story　torsional　response　of　the　structure　to　a　certain　extent,　but　there　is　a　larger　torsion　angle　in　the　isolation　layer.　Compared　with　the　ordinary　ground　motion,　SSI　effect　has　a　greater　influence　on　the　response　of　the　isolated　structure　under　the　far-field　long-period　ground　motion.　The　displacement　of　the　isolation　layer　may　exceed　the　limit,　and　the　overall　damping　effect　is　poor.　It　is　suggested　that　in　order　to　ensure　the　safety　of　the　base-isolated　structure　on　soft　soil　foundation,　the　SSI　effect　should　be　considered　in　the　design　of　structure,　and　the　adverse　effects　of　far-field　long-period　ground　motion　should　not　be　ignored.　©　2022,　Editorial　Office　of　Journal　of　Building　Structures.　All　right　reserved.