Aiming at the inference performance descending of CLINK algorithm in dynamic routing IP network,a kind of variable structure discrete dynamic Bayesian network model was established.Based on the simple model after in-troducing assumptions of Markov property and time-homogeneity,a kind of congested link inference algorithm VSDDB was proposed.Successive over relaxation iterative algorithm was introduced to solve the link congested prior probabilities,based on the Bayesian maximum a-posterior criterion,a kind of weighted heuristic greedy algorithm was used to infer the set of congested links.The experimental results have shown that the VSDDB algorithm has better in-ference performance.