Yangtianqing tailings dam is a new dam planned for a copper mine. At the design period, test in laboratory is carried out to simulate the process of dam pile based on the design information of Yangtianqing tailings dam. And the regularity of the saturation lines’ change at the condition of flood and normal is studied, when the dam have been heaped to the about 2/3 of the total height (120 m). Based on the test data, the stability coefficients of the dam at this height in different conditions are obtained with the Slide software, and they could be served for the following test and the mine’s future safety production. It is shown that the dam is safe in the normal condition, while in the condition of flood, the stability coefficient is less than the benchmark in national standard. Thus, it is necessary to rectify the preliminary design or to take other measures to ensure the safety of the tailings dam.