Abstract: In order to improve the accuracy of Multi Agent based fault diagnosis system for satellite and to make use of diagnosis information captured by every diagnosis method, technology of data fusion is introduced into Multi Agent diagnosis based on the analysis of fault diagnosis theory . Weights are introduced into fusion of diagnosis result according to the feature of satellite fault diagnosis. The improved Dempster Shafer evidential theory arithmetic and the method of weights calculating are given. At last, validity of the method is proved by an example given in this paper.