Abstract: In this paper,due considerations have been paid to the characteristic features and phenomena of the tremendous loess landslides induced by the 1920 Haiyuan earthquake (M s =8.5),the 1718 Tongwei earthquake (M s =7.5)and the 1654 Tianshui earthquake (M s =8.0).All of them occurred in the loess Plateau of Northwest China .Based on these features and phenomena such as large extents,high sliding speeds and long travelling distances,an inducing mechanism,e.g.the loess mass disintegration oblique projection collision between loess blocks and pulverization under the joint action of vertical and horizontal seismic acceleration is presented.Through dynamic deformation analysis,the whole process of loess mass obligue projection movement and the formulae of sliding speed and travelling distance of earthquake induced loess landslide are deducted.Earthquake triggered Huihuichuan loess landslide,Xiji county,Ningxia autonomous region of hui minority,is cited as an example to verify these formulae.The computed results quite agree with the evidences in the field.