Abstract: Based on several typical cases of tailing dam break during flood periods, the basic events relevant to the accidents of tailing dam break due to overtopping were clarified and generalized, such as seismic intensity beyond the designed value and ineffective flood discharging measures taken. The accidents of tailing dam break due to overtopping were studied introducing fault tree analysis including minimum cut sets, minimum path sets and structural importance. The results showed that the number of minimum cut sets that causes the accidents of tailing dam break due to overtopping is 54, thus revealing that such accidents are easy to take place; the number of minimum path sets that implies the prevention of such accidents is 4; and the calculated structural importance of relevant basic events means that hidden danger, poor design and inferior construction of dam, lack of routine maintenance and poor geological conditions, etc, all are crucial to the control and prevention of such accidents especially during flood periods.