Abstract: Taking Daguan giant ancient landslide as an example, the basic characteristics, deformation process and resurrection mechanism of the ancient landslide are analyzed in detail by using high-precision remote sensing interpretation, UAV survey, field fine-adjustment survey, indoor rock and soil mass test and numerical simulation. The landslide developed three gentle slopes, which were accumulated by multiple periods during the evolution of complex slopes in geological history. The 14C dating of organic matter in the deep slip belt reveals that the landslide developed about 35,000 years ago. The plane area of the ancient landslide is about 385×104m2, and the volume is about 2.1×108m3. According to the deformation degree, it can be divided into four deformation zones: the unloading deformation zone in the rear (Ⅰ), the severe deformation zone in the middle (Ⅱ), the creep deformation zone in the middle (Ⅲ-1, Ⅲ-2) and the air collapse and sliding zone in the front (Ⅳ). There are 40 secondary landslides in and around the ancient landslide, among which 4 are super large, 4 are large and 15 are medium. Under the influence of multiple factors such as rainfall, earthquake, geological environment and human engineering activities, creep deformation occurs in many parts of the slope at present. The numerical simulation results show that under the condition of one rainfall in 100 years, several secondary landslides slide on the ancient landslide, and the overall stability coefficient is 0.98, there is the possibility of overall sliding. Under the strong earthquake condition, there may be deep sliding in the front and middle and rear areas of the ancient landslide, and the overall stability coefficient is 0.93. In this paper, the deformation characteristics and reactivation mechanism of the ancient landslide are comprehensively analyzed by various means, which can provide reference for the research on the reactivation and disaster prevention and reduction of such giant ancient landslide in the canyon area.