Abstract: Decision rules based on rough sets and the relationship between the decision rule with modus ponens rule in the deductive reasoning are discussed in this paper. The attributes in decision table are reduced, and the values of attributes in decision table are made an interval via the soft computing of data mining, whereby finding a reducible implied pattern of the data, and choosing the representative, while deleting those redundant or superfluous decision rules in the decision table. And it can keep the original properties and functions of the decision table. The procedure of soft computing by developing an expert system for diagnosis and treatment in acupuncture and moxibustion in Chinese traditional medicine is also described. The system developed based on rough set approach is more theoretical and common applicable than that developed based on statistics and expert experience in 1987. It shows preliminary superiority via the clinical tests in the traditional Chinese medical science.