Abstract: According to the embedded Markov chain theory and the generating function，the paper analyzes a priority queue polling system in discrete time.It is introduced a service that the common queue use gated service and the high priority queue use twice gated service，and the average queue length and average polling period is explicitly obtained.

Key words: gated service, twice gated service, high priority queue, common queue, average queue length, average polling period

摘要： 采用嵌入Markov链和概率母函数的方法对门限服务优先级排队系统进行分析，提出普通队列和高优先级队列分别采用基本门限和二级门限的服务机制，得出了平均排队队长和平均查询周期的解析式。

关键词: 门限服务, 二级门限, 中心队列, 普通队列, 平均队长, 平均查询周期