Abstract: The failure of some high fill slopes in recent years has caused serious after-effects to the safety of mountain airports. This paper takes the No.12 landslide of high fill slopes in Panzhihua airport as an example to discuss the sliding mechanism and the reinforced countermeasures of a high fill slope in mountain airport. The geological background and basic features of the No.12 landslide in the high fill slopes and its pretreatment schemes are described. The phenomena and process of deformation and failure for the landslide are also introduced in detail. The analysis of formation conditions and influence factors as well as the numerical modeling has revealed the formation mechanism and evolution process of No.12 landslide. Research results show that the main reasons resulted in the landslide are the soft mudstone layer in the bottom of fill slope, the abundant groundwater in the fill slope, the unreasonable layout of pre-reinforcement piles and the inducement of storm rainfall. The mode of the formation mechanism of the No.12 landslide is summarized as push creepinglocking and progressive shearingbreak sliding and overlapping.