Abstract: Fault tree analysis is a practical failure analysis method. It is the concept of the diagnostic reasoning that matched bottom event is searched automatically by inputting the fault phenomenon. Then top event fault tree is generated and minimum cut sets are computed. The test flow is created according to the order of importance of minimum cut sets in which the users can be guided to find the fault part. Fault diagnosis of a radar transmitter is carried out by fault tree construction. This fault tree analysis can not only facilitate the reasoning in search for potential failure or fault diagnosis, but also further resolve the problem of knowledge acquisition and keep high efficiency of the expert knowledge with the integrity of the knowledge.