Abstract: FDEST—The general development shell for non-real Fault Diagnostic Expert Systems(FDES) based on the reliability analysis methods is introduced in this paper,there are strong inference and good openness,it can apply to establish FDES for varied military materiel and civilian products.At first,the structure and functions of the FDEST is described,and then,the reasoning method based on reliability analysis method-Fault Tree Analysis(FTA):forwards and backwards inference logic,supporting three imprecise arithmetic about Bayes,Mycin,Fuzzy and four relationship of fault logic;object-oriented and rule representation of knowledge,the supporting multimedia interpretation engine and fault process model(text,image,voice and video);Applying object-oriented technique to design and implement the software:dividing objects(FDEST object,knowledge object and FDFS object),object communications and system interface etc.key technique is discussed.