A　new　method　for　analyzing　the　seismic　response　of　arch　dams　in　time　domain　by　combining　the　viscous-spring　artificial　boundary　with　explicit　finite　element　method　is　proposed,　by　which　the　influence　of　radiation　damping　on　seismic　response　can　be　considered.　In　this　method,　the　input　of　seismic　waves　is　implemented　by　loading　the　node-force　histories　on　the　artificial　boundary　which　are　discrete　analytic　stress　histories　of　the　input-displacement　field　on　the　bottom　boundary　and　the　free　field　on　the　side　boundary.　This　method　not　only　avoids　the　numerical　unstable　phenomena　of　the　existing　combination　method　of　the　explicit　FEM　and　the　transmitting　boundary　in　high　and　low　frequency　but　also　has　highly　computational　accuracy.　The　seismic　dynamic　responses　of　the　arch　dam　in　Xiaowan　Project　are　calculated　by　using　this　method.