Abstract: Due consideration has been paid to the characteristic features and phenomena of the tremendous sliding displacements triggered by 1920 Haiyuan earthquake (M s =8.5) on gently inclined loess slope which is located in the loess terrace 4 along Qingshui River,Guyuan County,Ningxia Autonomous Region of Hui Minority, China.Based on the features and phenomena such as high sliding speeds,long traveling distance,loess falls,wave form topographic surfaces and liquefaction,a compound mechanism is presented with the help of field exploration,mechanial and dynamic tests of soil and computed results.That is,saturated loess under the first fossil soil liquefied,and the upper loess produced mass disintegration oblique projection collision between loess blocks,pulverization and loess fall.The traveling distance of gently inclined loess slope is calculated with the author’s formulae.The computed results quite agree with the evidences in field.