The　seismic　response　analysis　model　of　soil-structure　system　of　underlying　rigid　rock　base　soil　condition　is　a　＇semi-open　and　semi-closed＇　energy　system.　Compared　with　a　fully　＇open＇　energy　system,　the　analysis　model　of　the　＇semi-open　and　semi-closed＇　energy　system　employs　the　seismic　input　mode　of　an　intra-domain　inertial　force.　This　input　mode　is　exactly　the　same　as　that　in　the　seismic　response　analysis　model　for　the　rigid　rock　base-structure　system.　Different　from　that　of　the　structures　built　on　rigid　rock　base,　the　analysis　model　of　the　soil-structure　system　with　underlying　rigid　rock　base　soil　conditions　requires　consideration　of　the　influence　of　semi-infinite　soil　layers　on　the　truncation　boundaries.　Many　researchers　and　engineers　have　misunderstood　this　issue　by　assuming　the　effect　of　truncation　boundaries　is　only　an　issue　of　an　artificial　boundary　condition.　Consequently,　they　have　adopted　artificial　boundary　conditions　to　simulate　the　impact　of　truncation　boundaries　on　the　radiation　energy.　In　real　engineering　practice,　a　more　important　influential　factor,　i.e.　the　free　field　effect　of　the　soil　layer　of　underlying　rigid　rock　base　soil　condition　has　been　neglected　in　the　analyses.　In　order　to　clarify　this　issue,　based　on　the　direct　analysis　model,　the　seismic　analysis　method　for　the　soil-structure　interaction　of　underlying　rigid　rock　base　soil　condition　was　developed　in　this　study.　The　results　indicate　that,　in　a　typical　engineering　experience　scale,　omitting　the　free　field　effect　at　truncation　boundaries　would　not　obtain　reasonable　calculation　results.　©　2017,　Engineering　Mechanics　Press.　All　right　reserved.