Abstract: To accurately simulate the seepage characteristics of earth-rockfill dams during leakage, a test device is developed. The device can precisely control the test variables such as platform slope, water supply discharge, water temperature, etc. The device can realize the automatic check of the flatness of the side wall and the bottom plate, the automatic control of the flow control system and the temperature control system, the water circulation of various water supply and suction combinations, and piecewise or linear temperature rise and drop control of the upstream reservoir water, dynamic monitoring of dam body temperature field, volume deformation and pore water pressure. A clay core wall rockfill dam is selected as the research object, and the leakage tests on earth-rockfill dams are conducted. The results show that the leakage will change the seepage field and temperature field of the dam body, causing the surrounding temperature value to change significantly. With the gradual downward movement of the leakage area, the temperature value at the location increases significantly, the fluctuation of the saturation line and the seepage rate of the dam also increase, and the adverse conditions affecting the seepage stability of the dam body gradually increase. The test device can accurately simulate the real situation of various working conditions and the influences of multiphysics coupling effects on the leakage occurrence and development process of earth-rockfill dams, and it can monitor the evolution of various physical fields in the leakage development process in real time, providing an effective technical tool for the in-depth study on the seepage characteristics of earth-rockfill dams.