This　study　presents　a　substructure　method　with　good　accuracy　and　excellent　efficiency　for　seismic　underground　structure-dry　soil-saturated　soil-bedrock　interaction　problem　under　obliquely　incident　earthquake.　A　combined　zigzag-paraxial　on-surface　condition　attached　on　structural　surface　is　proposed　to　provide　the　dynamic　stiffness　of　structural　surrounding　media　including　dry　soil,　saturated　soil　and　underlying　half　space　bedrock.　The　on-surface　boundary　condition　can　be　implemented　to　any　desired　degree　of　accuracy　and　is　compatible　with　numerical　method　such　as　the　finite　element　method　and　the　finite　difference　method.　The　condition　is　then　coupled　with　structural　finite　element　scheme　and　seismic　wave　input　method　to　establish　a　substructure　method.　The　reliability　and　accuracy　of　the　proposed　substructure　method　are　verified　by　applying　it　in　two　degenerated　interaction　problems　and　comparing　with　other　solutions.　Finally,　the　proposed　substructure　method　is　employed　to　establish　a　lined　tunnel-dry　soil-saturated　soil-bedrock　interaction　model　for　evaluating　the　seismic　response　of　a　lined　tunnel　embedded　in　the　layered　half　space　rich　in　groundwater,　with　an　emphasis　on　the　effects　of　changing　groundwater　levels　on　seismic　response　of　tunnel　lining.