Lithium sulfur batteries are regarded as the promising energy storage device for its high energy density (theoretical: similar to 2600 Wh kg(-1)). In addition, the low cost of sulfur and its small impacts on the environment also arise tremendous interests of industries and governments. However, lithium sulfur batteries are still severely plagued by the free migration of intermediary polysulfides, which are the roots of lithium sulfur batteries' challenges. Besides various cathode design, carbon-based modification layers on the separator are also developed to enhance the electrochemical performance of the lithium sulfur batteries. In this study, carbon nanofiber/CoS/Ketjen black is successfully integrated on the commercial separator as an effective polysulfide blocker. It is demonstrated that the cell with a carbon nanofiber/CoS/Ketjen black-modified separator and high sulfur content (70 wt %) cathode can exhibit excellent stability with a capacity decay of 0.076% per cycle for more than 700 cycles under 1.0 C current density. Especially, the robust and flexible coating strategy can greatly expand the range of materials available to be integrated on the commercial separator.