The　reliable　numerical　simulation　of　the　landslide　process　contributes　to　the　establishment　of　evidence-based　disaster　mitigation　measures　in　seismically　active　zones.　To　achieve　this　goal,　a　simple　and　unified　state-dependent　shear　strength　model　of　discontinuities　is　presented　to　describe　the　shear　strength　degradation　in　a　seismic　landslide　process.　The　proposed　model　establishes　a　relationship　between　the　shear　strength　parameters　and　the　global　safety　factor　of　the　slope　by　assuming　that　the　slope　instability　(or　landslide　initiation)　is　accompanied　by　an　instantaneous　shear　strength　degradation　of　discontinuities.　To　realize　the　model　numerically,　the　algorithms　for　the　computation　of　global　safety　factor　and　the　modification　of　shear　strength　parameters　were　incorporated　into　the　discontinuous　deformation　analysis　(DDA).　Subsequently,　the　kinematic　accuracy　of　the　improved　DDA　method　was　validated　by　comparisons　with　theoretical　solutions　for　the　dynamic　sliding　of　a　block　on　an　inclined　plane.　Numerical　simulations　of　the　Daguangbao　landslide　triggered　by　the　Wenchuan　earthquake　were　performed　using　the　improved　DDA　method.　The　results　illustrate　that　the　shear　strength　degradation　of　discontinuities　affect　the　evolution　process,　travel　distance,　and　post-failure　shape　of　the　seismic　landslide　significantly.