Causal reasoning plays an important role in situation assessment (SA). Using Bayesian networks to find out the hidden patterns between situation hypothesis and events is the function needed to accomplish in situation as sessment. Based on different link relationship,a Bayesian network model for situation assessment is analyzed in this paper. To overcome the weakness of this model in application for dynamic changed scenario ,this paper presents an approach that uses a dynamic Bayesian network to represent features of the situation hypothesis and events. And the algorithms of propagation of corresponding information through the network are introduced respectively.