Landslides　are　one　of　the　most　common　geological　hazards　in　many　parts　of　the　world,　which　have　brought　catastrophic　consequences　to　mankind.　Seismic　shaking　can　be　an　important　trigger　factor　generally　resulting　in　large-scale　landslides.　For　some　paleolandslides　triggered　by　earthquakes,　despite　the　lack　of　historical　records,　certain　paleoseismic　parameters　can　be　back-analyzed.　In　this　paper,　the　discrete　element　method　(DEM)　was　applied　to　back-analyze　the　peak　ground　acceleration　(PGA)　triggering　the　Tahman　landslide,　a　paleolandslide　located　in　eastern　Pamir,　northwest　China.　Firstly,　detailed　field　geological　and　geomorphological　investigation　was　conducted　to　reveal　the　natural　and　seismic　characteristics　of　the　landslide.　Subsequently,　discrete　element　modeling　was　carried　out.　Simulation　results　suggested　that　the　Tahman　rock　slope　was　stable　under　natural　conditions.　Owing　to　arid　climate　and　water　shortage　of　the　study　area,　the　influence　of　water　was　ignored.　Additionally,　from　the　perspective　of　the　occurrence　time　of　the　landslide　and　geomorphologic　feature　of　the　deposits,　the　landslide　was　not　caused　by　glacier　activity　and　freeze-thaw　events,　and　thus,　must　have　been　triggered　by　an　earthquake.　A　peak　ground　acceleration　(PGA)　of　0.55　g　was　found　to　be　a　critical　value　for　triggering　landslides,　and　a　PGA　of　0.76　g　could　best　simulate　the　kinematic　process　of　a　landslide　when　the　simulation　results　were　calibrated　against　the　current　geomorphological　features　of　the　landslide　deposits.　It　can　be　concluded　from　the　present　study　that:　(1)　PGA　amplification　in　the　rock　slope　was　related　to　the　topography　during　earthquake　excitation;　(2)　the　effective　duration　of　the　seismic　wave　had　a　considerable　impact　on　the　back-analyzed　PGA,　which　decreased　with　increasing　effective　duration;　and　(3)　the　long　runout　of　the　Tahman　landslide　was　due　to　its　large　volume　and　the　interaction　of　the　slide　mass　with　moraines.