To improve the efficiency of fire damage assessment, the theory of Bayesian networks is evolved, on the basis of system analysis of damage information resource and correlativity, damage assessment model based on the Bayesian networks is constructed, the research includes the constitution, the probability estimation and the renewal of model based on the Bayesian networks. Finally, discuss the renewal process. The result shows that the model can be assessed by system, the damage effect based on damage information resource and the efficiency of damage assessment can be increased.