Abstract: Most of the slopes of open pit mines are finite slopes. The length of slopes is generally less than 200m. It is difficult to accurately evaluate slope stability by traditional two-dimensional slope analysis method. For the near-horizontal open pit mine, the end gang is a typical finite slope excavation-backfilling process. According to the characteristics of open-pit coal mine slope, the dynamic development law of pressure arch is revealed. The finite slope combined pressure arch model is established. The criterion of combined support arch instability is given. Through numerical simulation, the results show that the slope stress is toward mining. The center of the groove is unloaded, which is characterized by a time-sensitive asymmetric "pressure arch" shape. The timely follow-up of the inner tube can improve the stability of the end slope. The main mechanism is that the inner step provides effective support and prevents the end. The creep development of the slope limits the unloading space of the ground stress, buryes the position of the slope with large deformation, and transfers the stress concentration area to the inner step surface.