As one of the most important techniques in the 21st century, Wireless Sensor Networks(WSNs) receive a universal attention to the research on its key techniques. A solution is urgently expected to meet the higher-quality service requirements of new applications on the limited bandwidth of wireless networks. This paper proposes a scheduling Algorithm fit for the MAC scheme of WSNs, which has made possible the polling service capable of differentiating services of the cluster head node of two

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... ity levels. The theoretical model of this scheme is established through Markov chain and probability generating function. Mathematical analysis is made on the mean queue length, the mean inquiry cyclic time. It turns out that the findings from theoretical analysis correspond well with those from simulated experiments.