The occurrence of accumulation landslides in the edge of the Qinghai-Tibet Plateau is closely related to the effect of geological structures, heavy rainfall, and earthquakes, many of which are large-scale high-position accumulation landslides. To explore the mechanism and stabi-lity of large-scale high-position accumulation landslides, the Jiangdingya landslide in Zhouqu County was taken as the research object. The general situation and causes of the landslide were first analyzed from its geographical location and geological conditions. Then, the landslide calculation models were divided based on the traditional transfer coefficient method, and the variable slope method for landslide stability analysis was proposed. Finally, Midas GTS NX software was used to simulate and analyze the stability of Jiangdingya landslide under natural conditions, and the results were compared with the results of traditional and improved algorithms. The results show that: (1) Topographic slope, stratigraphic lithology, active faults, and historical strong earthquake in the study area are the internal causes of the landslide. The external causes are the mechanical strength reduction of rock and soil due to continuous heavy rainfall, the rise of Bai-long River water level and acceleration of flow velocity at the front edge of the landslide caused by rainstorm, the instability of the front edge, and the traction sliding at the middle and rear edges of the landslide. (2) When using the transfer coefficient method to calculate the landslide stability, the change of sliding surface inclination greater than 10° will lead to large errors in the result, so the improved variable slope method was proposed, and the numerical simulation were carried out on the Jiangdingya landslide to verify the effectiveness of the method. (3) The simulation results under natural conditions indicate that: the front edge of the landslide mainly shows horizontal slip and uplift, and the middle and rear parts of the landslide mainly show vertical subsidence. Therefore, large displacements occur in some areas of the landslide, indicating the possibility of local sliding. However, the displacement in other areas is small, and the landslide is in a stable state as a whole. The research results can be used as a reference for the stability analysis of large-scale high-position accumulation landslide.