The development of high-performance electric vehicles depends on high energy density Li metal batteries. However, the growth of Li dendrites causes the typical safety issue with respect of Li metal batteries, which is an obstacle to its commercial application. In this work, we prepare a flexible and tensile polymer coating on Li metal surface, which induces the uniform and dendrite-free deposition of Li metal during cycling. The combination of 18-Crown-6 and polyvinylidene fluoride synergistically allows for the robust flexibility and the high conductivity of Li ions of the prepared coating film. The composite polymer film suppresses lithium dendrites obviously. Results show that polymer coated on electrode has a high coulombic efficiency (similar to 97.38% after 200 cycles) and a good cycle stability.