Rainfall is a significant factor leading to failure of tailings dams. The impact of rainfall on the instability of dams is mainly reflected in the variation of negative pore-water pressure (i.e. matric suction) during rainfall infiltration. However, there is a lack of study on the effects of rainfall on suction in tailings dams. In this study, the response of suction to artificial heavy rainfalls in a tailings dam was investigated. The effects of rainfall intensity and surface vegetation conditions on the response of suction were studied. It is found that suctions at a certain depth in the tailing dam were kept constant until the wetting front reached this depth. Once suctions were altered, the values dropped rapidly. The magnitude of suction change generally decreased with depth. Rainfall infiltration mainly occurred above the depth of 40 to 80 cm when subjected to rainstorm and heavy rainstorms. Larger rainfall intensity leads to shorter response time and to larger depth affected by rainfall, implying that the tailings dam is more susceptible to shallow landslide failure under larger rainfall intensity. The existing vegetation increases infiltrability significantly and then produces an adverse effect on the stability of the tailings dam. On the other hand, it is observed that the presence of vegetation greatly prevented surface erodibility and then decreases the possibility of debris flow.