Abstract: Combining distinct sources of evidential knowledge in support of a ranking can improve the retrieval performance effectively.Adopting synonym-based evidence to extend the basic belief network can obtain an extended belief network retrieval model.The extended model uses different strategies to combine evidences leads to different ranking computation formulas，then influences the retrieval performance.This paper gives conjunctive combining algorithm based on disjunctive combining algorithm，and some proper modifications are given as to the conjunctive combining algorithm.Experimental results indicate that the retrieval performance based on conjunctive algorithmis higher than that based on disjunctive algorithm.