Abstract: Based on successful experience and lessons of dam collapsing in the process of dam system building and running, undermost board theory of flood control criterion of dam system is put forward through scientific generalization. It will exert a strongly theory oriented effect on dam system developing healthily and stably. The occurring odds of dam system destroyed by water can be forecasted according to its characteristic and innovation, especially chain dam collapsing. The unique meaning of flood-control criterion of dam system in theory is indicated by the theory, according to it, dam system construction can be brought into the scientific and standard process, and development of dam system security and steady can be promoted. Dam types of flood-control and the meaning of whole dam system safety were clarified. The calculation methods of flood-control ability in actual dam system units and distinguish of revising security of flood-control were also introduced. The application of the theory in evaluation of flood-control ability and reinforce and matching of dam system were indicated too.