The conflict appearing while combining several uncertain information reflects the degree of conflict between their sources. This conflict can be managed before the combination step by discounting belief functions using sources' reliability. In this paper, we suggest a generalized method for sources' reliability estimation based on distance measure and taking into account all its belief functions stored in an evidential database. This method is evaluated on real radar data and supplied good results in terms of sources' reliability improvement. Our method insures also the same level of relative reliabilities for all belief functions supplied by the same source and this level reflects the source's global reliability.