Abstract: A new type nanofiber separator with coaxial structure for lithium ion battery was constructed through electrospinning method. Polyether imide (PEI) was adopted as the core layer material due to its high heat-resistance and high strength, and polyvinylidene fluoride (PVDF) with excellent electrolyte affinity and interfacial stability was adopted as the shell layer material. The structure and performances of PEI-PVDF coaxial separator were investigated by SEM, TEM, TGA, electrochemical workstation, and battery test system. The results show that PEI-PVDF coaxial fiber has a clear core-shell structure. Compared with the commercial separator, it has excellent thermal stability and does not shrink after treated at 180℃ for 2 h. The liquid electrolyte absorption rate also increases greatly, and reaches up to 520%. The electrochemical stability window is up to 5.0 V. The ionic conductivity is 2.3 mS·cm^-1. The lithium ion battery assembled with PEI-PVDF coaxial separator still show the specific discharge capacity of 107 mAh·g^-1 at discharge current density of 8 C. In the recovery at 0.2 C rate, the specific capacity retain 95.4% of its original specific capacity. The coulombic efficiency of the batteries is 92.5% after 100 cycles of charge and discharge. The characteristics of the high rate and high heat resistance of the PEI-PVDF separator show that it is a kind of high power, high safety separator for lithium ion battery.