Abstract: Since the 1960s, a large number of irrigation systems have been constructed to solve the agricultural drought problems in the loess area. At the same time, the irrigation has induced a lot of loess landslides. At 20:00 on January 28, 2015, a medium-sized loess landslide occurred in Jiaojia Village, Heifangtai table-land, Yongjing County, Gansu Province, northwestern China. The landslide seriously affected the safety of No.309 national road and Liupanxia Reservoir that were below Jiaojia No.4 landslide. Based on the investigation of fracture distribution and hydrogeology, combined with research techniques such as low-altitude photogrammetry, high-accuracy engineering geological mapping and triaxial test, the basic characteristics of Jiaojia No.4 landslide were analyzed, and the formation mechanism of the landslide was preliminarily understood. The preliminary results showed that: ①Before the occurrence of the landslide, there are obvious deformations of trailing-edge fractures; ②The sliding distance of the loess landslide is 548.3m，the sliding volume is 15.35×104 m3 and the sliding area is 6.6×104 m2; ③ The stress-strain mode of saturated loess is characterized as strong strain softening and shear shrinkage, as well as a certain of static liquefaction; ④ The landslide is caused by static liquefaction of saturated loess layers.