Abstract：The basic conditions, which the dam system can come up to relative stability, are as follow. First, the coefficient of relative stability must be equal or larger than a certain permissible value, which is the key to achieve the goal. Then there must be enough storage capacity of flood control, and last the dam system must be safe without disease and danger. In the same time it should be satisfied with these conditions. The harvest in the dam land can be ensured under the standard of storm flood once in twenty years. When the silt area has come up to design silt area, the average silt thickness will be smaller than 20cm. The control methods of stability are rational arrangement of dam system scale and the order of construction, balanced distribution of storm flood persisting in slope control, raising the degree of watershed control, fixing up the flood carrying channels to prevent water logging at the dam land and flood exceeding the standard, as well as enhancing routine maintenance.
2005, Vol. 3 
