The invention relates to a fault diagnosis rule extraction method, in particular to an imperfection fault diagnosis rule extraction method based on the quantitative characteristic relation. The method solves the problem that according to an existing imperfection fault diagnosis rule extraction method, fault diagnosis rules cannot be extracted from a decision table containing various unknown attribute values, solves the problems that according to the existing imperfection diagnosis rule extraction method, similarity degrees among examples are not considered, and the similarity relation among the examples is not measured, and solves the problem that original information will change due to an existing manual data filling process. The imperfection diagnosis rule extraction method based on the quantitative characteristic relation comprises the steps of (1) preprocessing original imperfection fault diagnosis data, (2) determining the type of an unknown attribute value, (3) analyzing an imperfection fault diagnosis decision table, (4) conducting reduction, and (5) extracting fault diagnosis rules. The imperfection fault diagnosis rule extraction method is applied to the field of fault diagnosis rule extraction.