In　the　numerical　simulation　of　wave　problems,　it　is　often　necessary　to　truncate　the　unbounded　computational　domain　at　a　finite　distance　to　reduce　the　requirement　of　computational　resources.　To　manage　this　truncation,　artificial　boundaries　are　introduced,　among　which　the　Scaled　Boundary　Perfectly　Matched　Layer　(SBPML)　is　regarded　as　a　reliable　strategy.　In　this　paper,　we　implement　the　SBPML　element　into　the　commercial　software　ABAQUS　using　the　User-Defined　Elements　(UEL)　subroutine.　The　key　equations　of　the　SBPML,　the　procedures　of　meshing　for　the　SBPML　domain,　and　the　implementation　workflow　of　the　subroutine　are　given　in　details.　Four　benchmark　examples　of　wave　propagation　problems　in　unbounded　domains　are　presented　to　demonstrate　the　accuracy　and　effectiveness　of　the　proposed　method.　Furthermore,　the　application　of　the　UEL　in　nonlinear　seismic　soil-structure　interaction　analysis　is　demonstrated　by　evaluating　the　seismic　response　of　a　five-layer　alluvial　basin　in　a　homogeneous　half　space　and　an　aboveground-underground　integrated　structure-multilayer　soil　system　under　obliquely　incident　earthquake　waves.　Using　the　proposed　UEL,　all　wave　propagation　analyses　can　be　directly　implemented　in　ABAQUS　with　a　seamless　workflow.　To　facilitate　the　use　of　the　proposed　approach,　the　codes　of　the　UEL　are　published　in　an　open-source　format.