Considering the limitation of the existing methods and the problems to arise when evidence theory is introduced to rule fusion, a method of fusing the decisions of multi-reduction sets based on evidence theory is proposed, the concrete procedures of the method are described and the application analysis of the method is done on the aero-engine fault diagnosis samples. The result shows that by using the method the problems of reluctant decision of single reduction set, of the instability of identification-rate between all the reduction sets and of the high conflict of the single attribute decision are eluded. This provides a scientific decision foundation theoretically for aero-engine fault diagnosis. The dominance of the method is summarized in the conclusion.