A lot of experiment data are produced during the process of equipment development, therefore exploiting these data by the data mining instrument becomes an important issue. Bayesian network is then proposed. And the approach, which is used in the study course of Bayesian network and is based on the information theory, is improved by the statistics knowledge, and the topology of Bayesian networks is constructed. Combined with the concept of extended Markov blanket, a method to determine the faulty unit is presented. The conditional probability table of Bayesian network can also assist the personnel in finding out the defect of design.