Lithium-sulfur (Li-S) batteries have attracted considerable attention as one of the most promising power sources due to the higher energy density, lower cost and better environmental friendliness. However, Li-S batteries still face a challenge of unsatisfied cycle life due to the so-called “shuttle effect”. Here, a 3D light-weight and porous C3N4 nanosheets@reduced graphene oxide (PCN@rGO) network is prepared to overcome the barrier. The 3D PCN@rGO network can not only firmly anchor polysulfides by strong chemical adsorption, but also offer fast electron and mass transfer paths to enhance kinetics of redox reactions. Meanwhile, the 3D network can hinder aggregation of C3N4 nanosheets or rGO nanosheets to remain a high surface area. As a result, the PCN@rGO cathode delivers high reversible capacities of 1205, 1150, 986, 800, 685, and 483mAhg−1 at the rates of 0.1, 0.2, 0.5, 1, 2, and 5C, respectively, and the cathode still delivers a specific capacity of 680mAhg−1 at 0.5C after 800 cycles, demonstrating a very low capacity decay of 0.048% per cycle. The exploration of this light-weight polar C3N4 as a sulfur host provides a promising choice to achieve high energy density and long cycle life Li-S batteries.