Abstract：Malingyan Landslide is located in the left bank of Tongkou River，which is 4 km away from the upstream of Tangjiashan dammed lake. Because of its special location，it receives much concern in the process of dealing with an emergency of the dammed lake. Based on the field geological investigations of basic landslide geological conditions，deformation and failure characteristics before and after Wenchuan 8.0 earthquake，stability of Malingyan landslide，especially after the formation of dammed lake，is analyzed. The results show that the landslide is generally stable after earthquake，but part of the former section of the upriver is possibly instable because of earthquake and water storage of the dammed lake and so on. Malingyan landslide will not put against Tangjiashan dammed lake and the comprehensive treatment at a disadvantage in the future can be saved，but more attention should be put on the former section of the landslide as it may be partially instable as a result of continuous rainfalls as well as the earthquakes. And then，the potential sliding on the upside may be harmful to some residents on the slope body. Based on analytical stability results of Malingyan and the other landslides in earthquake areas，the overall reactivation of the large-scale ancient landslide caused by earthquake is mainly controlled by its terrain slope and micro-geomorphic characteristics. The whole or part ancient landslides triggered by earthquake will be instable if it satisfies the sufficient condition，in which the terrain slope is above 40° as well as slow part changes into steep one. Not all ancient landslides are possibly reactivated by the earthquake，and this will tremendously change the common misunderstanding in the past that the earthquake will trigger the whole ancient landslide reactivated inevitably.
