Polymer　electrolytes　are　one　of　promising　candidates　that　can　meet　the　demands　of　high　safety　and　stability　of　high-energy　lithium　metal　batteries.　However,　the　practical　applications　of　polymer　electrolytes　are　usually　limited　by　the　low　ionic　conductivity,　narrow　electrochemical　window　and　highly　interfacial　resistance.　Here　we　designed　a　poly(vinyl　ethylene　carbonate)　polymer　electrolyte　for　polymer　lithium　metal　battery　by　in-situ　polymerization　method.　The　new　polymer　electrolyte　provides　superior　ionic　conductivity　with　2.1　x　10(-3)　S　cm(-1)　at　25　degrees　C,　wide　electrochemical　window　up　to　4.5　V　(vs.　Li+/Li)　and　excellent　interfacial　compatibility　to　electrodes.　The　ions　transports　are　mainly　achieved　from　the　coupling/decoupling　between　Li　ions　and　oxygen　atoms　in　C=O　groups,　partially　from　the　coupling/decoupling　between　Li+　and　oxygen　atoms　in　C-O　groups,　and　probably　moving/exchange　of　Li+　between　C=O　and　C-O　groups　in　the　process　of　segmental　motions　in　high　and　low　molecular　polymers　of　polymer　electrolyte.　The　lithium　metal　batteries　with　LiFePO4　cathode　can　deliver　a　high　discharge　capacity　of　similar　to　165　mA　h　g(-1)　at　25　degrees　C,　and　even　similar　to　104　mA　h　g(-1)　at　-15　degrees　C　with　current　density　of　0.1C.　Therefore,　the　novel　polymer　electrolyte　designed　in　this　study　is　a　promising　candidate　for　high　performances　polymer　lithium　metal　batteries.