Decompiling, as a means of analysing and understanding software, has great practical value. This paper presents a kind of decompiling method offered by the authors,in which the techniques of library-function pattern recognition, intermediate language,symbolic execution, rule-based 4ata type recovery program transformation, and knowledge engineering are separately aPPlied to diIfernt phases of decompiling. Then it is discussed that the techulques of developing expert systems are adopted to build a decompiling system shell independent of the knowledge of language and program runningenvironment. The shell will become a real decompiler, as long as the new knowledgeof application environment is interactively acqired. This paper presents a kind of decompiling method offered by the authors, in which the techniques of library-function pattern recognition, intermediate language, symbolic execution, rule-based 4ata type recovery program transformation, and knowledge engineering are separately aPPlied to diIfernt phases of decompiling. Then it is discussed that the techulques of developing expert systems are adopted to build a decompiling system shell independent of the knowledge of language and program runningenvironment. The shell will become a real decompiler, as long as the new knowledgeof application environment is interactively acqired.