The loess Plateau of northwestern China is located in a semiarid climate region with the maximum precipitation of less than 700 mm, but it is one of the areas with most serious landslide hazards in China. Landslides on the loess Plateau are both of large number and large scale, including numberous recent landslides formed in earlier Holecene and ancient landslides formed in Latc Middle Pleistocene. Among the factors controling the landslides on Loess Plateau Hipparion(N2) laterite servcs as a medium and sliding zone and plays an important role in formation of large and medium scale landslides on the Loess Plateau of northwestern China. Based on the predecessors studies, and recent reseach by authors, this paper summarizes the formation and development regularities of large and medium scale landslides on the Loess Plateau, the effect of soil mass structure on formation of landslides, the relation of landslides with material composition and engineering properties, and ancient weathered zone (unconformable surfacc) of Hipparion laterite. Finally the formation mechanism of landslides is discussed.