By means of the coincidence degree theory,we studied the existence of positive periodic solutions for a ratio-dependent predator-prey system with Holling Ⅲ.A set of sufficient conditions for the system to have at least one positive periodic solution was established.%应用重合度定理研究一类比率依赖 Holling-Ⅲ的捕食-食饵系统的周期解的存在性问题，建立了该系统具有至少一个正周期解的充分条件。
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