On the basis of properties analysis of disaster chain, the assumption of connotation and extension of systematic natural disaster chain is clarified. Therefore the natural disaster chain structural model in the form of mathematical language is defined, and the relation and property of the structural model is studied. According to the analysis of the mathematical model of disaster chain, it shows that the disaster chain is caused and dominated by both the outside environments and structural relation of inner state. The outside environment influence is the gestation of disaster and the interaction of inner state is the necessary condition of disaster chain. The disaster mitigation mode is studied from the point of both sides, and the emphasis is on the inner structural relations chain-cycle. An example in view of snowstorm in 2008 is presented to apply and verify the above theory.
