Based on the related theory of natural disaster chain, the author studies the related subjects consisting of social unexpected event chain at first, classifies the chain into such two periods as implicit chain and explicit chain, based on this, analyzes the reaction mechanism of social unexpected events, and puts forward the interdiction mechanism for preventing social unexpected events from macrolevel such as forecast before the events, the increase of systematic threshold value, interrupting the chain to avoid the risk, weakening negative energy value and so on through constructing social unexpected event incidence model, in order to provide theoretical reference for governments to further respond social unexpected events.