The safety operation of tailings dam is the necessary conditions to ensure that the tailings dam is steady. Field investigation and sampling of a tailings dam were carried out in Jiangxi Province. The dam composite and tailings deposition law are discussed in this paper. Dam stability was studied under different working conditions and the disaster prevention measures were discussed. The research results indicate that: the change trend of the tailings in the tailings dam for outer to inner is very obvious from coarse to fine while that from top to down is not. The change is slow in the deposited beach and the slope relatively flat. There is no tailings mud in the tailings dam. The calculated safety factor under normal or operation condition and flood operation condition could meet the standard requirements on the stability of the dam. However, the safety factor is far lower than the standard requirements on that under the full saturation condition and seismic condition. The stability of dam is reduced significantly, which may lead to the instability of the tailings dam.