Abstract: Due to the strong water sensitivity of loess, loess landslide dams are highly susceptible to breach and damage under the influence of water. To understand the downcutting and damage process of loess landslide dams under different upstream water flow rates, a series of five flume tests with varying flow rates(0.6 L·s^-1, 0.8 L·s^-1, 1.0 L·s^-1, 1.2 L·s^-1 and 1.5 L·s^-1) were conducted. The test results show that: (1)The downcutting process of loess landslide dams can be divided into three stages: the scouring stage, erosion stage, and damage stage. (2)Loess landslide dams under different upstream flow rates exhibit similar downcutting processes, but the final damage patterns differ. Overtopping occurs when the upstream flow rates are 1.2 L·s^-1 and 1.5 L·s^-1,while piping occurs at flow rates of 0.6 L·s^-1, 0.8 L·s^-1 and 1.0 L·s^-1. (3)The downcutting process is most pronounced during the scouring and erosion stages. As the flow rate increases, the seepage time decreases and the erosion rate increases, making the backwater slope of the dam more susceptible to erosion damage. Conversely, at lower flow rates, the seepage time is longer, the erosion rate is smaller, and the loess landslide dam is more prone to the formation of a piping surge channel due to seepage.