Abstract: The K129 landslide is located on the ancient landslide which lies on the east of meihua village of qingtong town in Zhen'an county, Shaanxi. Due to constructing highway, a high slope was cut in the front of the ancient landslide. The cut volume was of 6.0?04m3.The ancient landslide was relived because no stabilizing measures were adopted in October, 2009.The deformation developed very quickly, and caused the road pavement to heave, the retaining wall to crack. If the whole landslide moved down, not only Xi'an-an'kang highway and Highway 102 were interrupted, but also Qianyou river jammed. The jam would be formed a landslide dam and a lake which would threaten the lives and property of the peoples round the river. In view of the landslide, on the basis of geologic analysis, authors investigate the landslide failure modes. It was found that the formation of landslide control factors was the fragile geologic framework composed by the silty clay mixed stone fragments and phyllite and water-rock reaction. Rainfall was the main factor inducing the landslide. Engineering excavation weakened the locked segment of landslide, accelerated the landslide deformation. Meantime, the characters of the deformation rate and spatial deformation in the landslide were reflected by the displacement monitoring datum and construction feedback information. Namely the landslide belonged to the bedrock interface landslide. The primary character is the back force. The minor one is the foreside pull. According to the study data, the emergency measures, design and construction options were adjusted in time, which ensured that the landslide treatment was completed successfully.