考虑可重入生产系统除第一个外均为有限缓冲区的情形 ,建立了两种两站四缓冲区的拟生灭过程 ( QBD)型模型 .系统在随机调度策略下状态集是不可约的 ,而在最后一个缓冲区先加工 ( LBFS)的策略下状态集是可约的 .将可约的状态集化成不可约的吸收集和可约状态集的和 .求出了系统状态的稳态分布 ,给出了系统稳定的充要条件 Considering the case of a reentrant production system except for the first one, which is a finite buffer, two quasi-birth and death process (QBD) models of two stations and four buffers are established. The state set is irreducible under the random scheduling strategy , And the state set is definable in the last buffer-first-process (LBFS) strategy. The set of reducible sets is the sum of irreducible sets of absorbable and contractible states. The stability of the system state State distribution, given the necessary and sufficient conditions for system stability