To solve the problem of imbalance of resource demand and supply in emergency process, this paper redefines the elementary cell of GERT network in emergency process, establishes the GERT combining the natural evolution of disaster and the action of emergency rescue, designs the maximum entropy model for solving the emergency state shift probability, simplify the GERT network and proposes the algorithm for optimal allocation of resources. This research provides the framework and tools for the allocation of resources in the way of qualitative and quantitative analysis. Meanwhile, it offers a new methods and ideas for the forecasting and evaluation of the disaster evolutionary tendency.