Abstract: SDG is an important technology of building qualitative model.The signed directed graph(SDG) is an important research branch of the fault diagnosis field,with a lot of application and development prospect.For the reciprocating compressor,this paper puts forward a comprehensive SDG fault diagnosis structure.The comprehensive fault diagnosis structure takes the modeling method based on the experience knowledge,introduces the idea of hierarchical modeling and the bidirectional inference method based on assumptions-verification.The research shows that this method has strong ability of fault diagnosis.