Dempstershafer evidence theory has been used widely in civil aircraft electrical system fault diagnosis. However the combination of highly conflicting remains a difficult problem in practical applications. In order to solve the problem, a new method is proposed in this paper．The proposed method in this paper introduces the historical data as modifying factor, modify the evidences, and verify the diagnosis method by classical data case. Data case validation results show that the new method can identify the target more quickly and accurately, and improve the reliability and accuracy of fault diagnosis results. This new method enhance the performance of the system and is a breakthrough in the engineering application of DS evidence theory.