The stability analysis for a typical tailings dam is carried out by combining the fluid-solid coupling method with the strength reduction method. Then the seepage field

the location of potential sliding surface and the safety factor are determined; and the tailings dam failure criterion in strength reduction method for tailings dam is suggested. By comparison

the location of the saturation line by the above determined seepage field is in accordance with the field measured saturation line; meanwhile

the location of the potential sliding surface and the safety factor is well consistent with the results by Bishop method

so as to show the feasibility of the stability analysis for the tailings dam by combining the fluid-solid coupling method with the strength reduction method. Based on the above results

the instability model of the tailings dam is studied; and two instability models are concluded

one is the local instability which the instability takes place in the part of the tailings dam sliding; and the other is global instability which can cause the whole tailings dam failure. Moreover the main factors which lead to the two failure models are analyzed; and the result shows the important factor of the local instability is caused by the too shallow saturation line in the tailing dams.