Abstract: The conventional method for deformation monitoring of earth-rock dams based on a single point cannot acquire enough information. It doesn’t consider the position and the relationship between points. It cannot accurately monitor the real and three-dimensional deformations of the earth-rock dams. Owing to their complex structure and non-rigid character, the earth-rock dams exhibit irregular deformation when subjected to external force. So a new method for dam deformation monitoring based on three-dimensional laser scanning point cloud data is proposed. First, the absolute orientation is implemented for the point cloud data series collected at different time, allowing that the post-possessing can be performed in a unified coordinate system. Then, the cross-section point cloud data series at the same location collected at different time are compared and analyzed to figure out the dam deformation and displacement in horizontal and vertical directions. Jiangang Reservoir in Zhengzhou City is chosen to verify the accuracy and efficiency of the proposed dam deformation monitoring method. The experimental results show that the proposed method is highly accurate and real-time, and can meet the requirements of dam deformation analysis.