During the 1920 Haiyuan earthquake, numerous catastrophic landslides were triggered in the loess area on the northwest of China, killing about 200,000 people. Among them a landslide occurred in Dangjiacha area of Xiji County, Ningxia (termed as Dangjiacha landslide in this paper) was investigated in detail. This landslide originated on a slope of about 20 degrees, and the displaced soil mass from the source area traveled about 3200 m, damming a valley. Field survey revealed that standing groundwater exists within the landslide on the source area, and the loess on the source area was in great void ratio. Therefore, it is reasonable to infer that liquefaction failure within the water-saturated loess layer was the main reason for this long-travel landslide, rather than the assumption that these earthquake-triggered rapid landslides were due to the suspension of silt in air. To examine this assumption, ring shear tests were performed on the samples taken from the source area of Dangjiacha landslide. Undrained ring shear tests on the water-saturated loess soils applied to monotonic/cyclic shearing showed that the loess soil is highly liquefiable, and shear failure can be triggered during cyclic loading. In additional, undrained ring shear tests had also been performed on the dry sample “saturated” by air to examine whether landslide with high mobility can be triggered or not, with the involving of air. The results revealed that the increase of pore-air pressure with increase of shear displacement was small such that no significant reduction in the shear resistance was observed.