The topic of unrepairable system is an important content in system reliability theory. There are many reasons cannot be repaired, some because of technical reasons, cannot repair, some because of economic reasons, not worth to repair, and some because of making repairable system simplification. So it is essential to pay attention to unrepairable systems. In this paper, the lifetimes of unrepairable systems are considered as uncertain variables. Based on that, the fundamental mathematical models

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... of series systems, parallel systems, series-parallel systems and parallel-series systems are established, respectively. Furthermore, we make reliability analysis of above four unrepairable systems, respectively. Some numerical examples are also given for illustration.