Lithium-sulfur (Li-S) batteries are regarded as one of the great potential members for the next-generation rechargeable batteries due to their outstanding theoretical energy density (2600Whkg−1), low cost and environment friendliness. However, the further developments of Li–S batteries have been obstructed by the low electronic conductivity of active material and the diffusion of polysulfides. In this paper, we found a cheap raw material to prepare a nitrogen doped porous carbon (NPC) by a simple method. Then, NPC was used to modify the pristine separator to promote the overall performance of Li–S batteries. With the NPC modified separator, a high initial discharge capacity of 1382mAhg−1 at 0.2C and a low fading rate of 0.078% per cycle within 500cycles at 0.5C can be delivered by the pure sulfur cathode (1C=1675mAhg−1), which attribute to the high-content nitrogen doped level and large specific surface area of NPC. This shows a great potential for the scale-up applications of Li-S batteries.