Lithium metal battery with high specific energy and high safety is crucial for the next-generation energy storage technologies. However, the poor thermal stability, lower mechanical performance, and poor electrochemical performance of the commercially available polyethylene (PE) separator hinders the development of high-specific lithium metal batteries. Herein, a functional PE separator is prepared by innovative coating the TiNb₂O₇ microspheres with oxygen vacancies on the surface of PE (denoted as TNO_−x-PE). The porosity, contact angle, electrolyte uptake rate, thermal shrinkage rate, mechanical properties, conductivity as well as lithium ions transference number of the TNO_−x modified PE separator are all improved. The favorable TNO_−x is beneficial for facilitating fast Li⁺ migration and impeding anions transfer, guiding the uniform distribution of lithium-ion flux. Consequently, the lithium symmetric cells with TNO_−x-PE separator can be stably cycled more than 1600 h at 1 mA cm⁻², and the initial capacity of the LFP/Li cells with TNO_−x-PE separator is as high as 139.8 mAh g⁻¹, and after 500 cycles, the capacity retention rate is still 99.5%. This work may provide a new idea to construct a multi-functional separator with high safety and superior electrochemical performance and promote the development of LMBs.