Abstract: The heights of filling body in the North-east of Panzhihua Baoanying airport reach 128 meters, which is rare among the high slopes in China. The 12th Landslide has occurred 5 times sliding and 2 times strong deformation since the airport was built in 2001, and its cause of formation has always been doubtful. The formation and evolution process and influencing factors of the 12th landslide are analyzed and summarized systematically by collecting data. With the help of on-site investigation, monitoring, drilling and laboratory test, the mechanism of deformation and failure of landslide in recent two times is revealed emphatically. The results show that internal factors of the slope sliding many times include special groove topography, abundant underground water in the slope and special rock mass structure, and rainfall, earthquake and surcharge are the external factors. The mechanism of the last two deformations can be summarized as the thrust-type sliding caused by the resistance of the front of the anti-slide pile and the loading of the trailing edge, and then turns to creep-cracking fracture failure mode under the action of groundwater softening. The corresponding prevention and control countermeasures are put forward and the results of the study provide a useful reference for the understanding of multi-stage and secondary sliding mechanism of high fill slope and engineering treatment。