Abstract: Many fields, such as data fusion, expert system and aritificial intellgence,etc, need nondeterministic ways to perform fuzzy reasoning. The method for computing the conclusion's synthetical certain factor when multi-hypotheses are applied in the same conclusion is one of the important nondeterministic reasoning ways. This paper proposes such a method which is availabe whether the weights of all hypotheses are same or different. The method is proved to be an effective reasoning and computing way in the engineering practice,especially in the fileds of data fusion and expert system.