Abstract: Aiming at the problems of traditional slope deformation monitoring, such as high cost, high risk and low automation, which rely on manual layout of marker points, an automatic monitoring method based on UAV photogrammetry was proposed. Multi-rotor UAV was equipped with high-resolution camera and RTK/IMU positioning technology to obtain multi-period close-up photographic images of the target slope and generate 3D models and orthographic projection images. A series of corresponding image points were identified by automatic image registration, and the 3D coordinates of the corresponding image points were obtained via Triangulated Irregular Network (TIN) interpolation, and the displacement was obtained by comparing the 3D coordinate differences in different periods. A case study on the right bank slope of the Shenyu River, a tributary of Jinsha River showed that this method eliminated the need to place monitoring markers on the slope surface, reducing the risk and cost of manual layout, improving monitoring efficiency and accuracy, enabling automatic areal monitoring and accurately reflecting the overall deformation of the slope surface. The research results can provide a safe, efficient and reliable way for slope deformation monitoring and has broad application prospects.