Abstract: Through a thoroughly analysis to system-level load- strength interference relationship, the problems of information loss in the process of conventional component reliability analy- sis and modeling are discussed, as well as the reason why it is impossible to construct dependent system reliability model sim- ply by means of component reliability parameter. Further more, the mechanism of common cause failure (CCF) of k/n(F) syst- em is discussed. It is shown that the randomness of environm- ent load is the “root cause” of common cause failures. CCF involves concepts, such as “root cause” and “coupling mechan- ism” which are interpreted mathematically from the viewpoint of random environment load bringing about failure dependency. Opinions about “inherent dependency”, “additional dependency”, “absolute CCF” and “relative CCF” are presented and discussed. At last, an approach is presented to develop discrete common cause failure probabilities model based on the loadstrength interference analysis of system-level.

Key words: Common cause failure System reliability, Failure probability, Redundant system