Abstract: In view of problem of higher misdiagnosis rate in fault diagnosis system of power grid based on single criterion, the paper proposed a design scheme of fault diagnosis system of power grid with multi-criterion fusion decision based on DS evidence theory. The scheme uses three criterion methods of threshold method based on value distinguishing, threshold method based on current differential and threshold method based on power direction to judge a section of data of fault recorder, and makes fusion for judging results by use of DS evidence theory, so as to judge fault type and fault position accurately. The example analysis showed that the scheme can improve accuracy of fault diagnosis of power grid effectively.