Due　to　the　complexity　of　the　model　and　the　long　duration　of　earthquake　records,　the　nonlinear　dynamic　analysis　of　arch　dams　consumes　a　lot　of　calculation　time.　In　this　paper,　an　earthquake　record　truncation　method　based　on　the　acceleration　response　spectrum　(ARS)　is　proposed　to　save　the　calculation　time　of　nonlinear　dynamic　analysis　of　arch　dams.　The　nonlinear　dynamic　responses　of　the　210m-high　Dagangshan　dam　of　China　are　performed　as　a　numerical　example.　Firstly,　the　statistical　relationship　between　the　Arias　intensity　(AI)　and　ARS　is　investigated　using　a　large　number　of　actual　ground　motion　records.　Secondly,　the　spectrum-based　earthquake　record　truncation　method　is　proposed.　Finally,　the　accuracy　of　the　proposed　method　is　verified　using　the　actual　earthquake　records,　and　the　efficiency　of　the　proposed　method　is　compared　with　the　AI-based　method.　Analysis　results　show　that　the　proposed　method,　considering　the　structural　characteristics　of　the　arch　dam,　can　save　more　calculation　time　than　the　AI-based　method,　while　ensuring　a　sufficiently　accurate　calculation　result.