Abstract: In view of problems of high cost and low reliability of existing protection methods of mine PON network, the paper designed a new type of splitter composed of three beam splitters. The new splitter adds a beam splitter with splitting ratio of 50∶50 to traditional splitting, and uses its characteristics that insertion loss of up and down optical path is consistent to achieve protection of mine PON ring network by optical network units with single PON port. It avoids the use of redundant controllers and optical network units with dual active PON ports, and has high reliability and low cost.