To meet the requirements of both high energy and power density with cycle durability of modern EVs, a novel nano-sulfur granular assembled film coated on the three-dimensional graphene sponge (3D-GS) composite is prepared as a high performance active material for rechargeable lithium sulfur batteries. Instead of conventional graphene powder, three-dimensional rGO sponge (3D-rGO) is employed for the composite synthesis, resulting in a sulfur film directly in contact with the underlying graphene layer. This significantly improves the overall electrical conductivity, strategically addressing challenges of conventional composites of low sulfur utilization and dissolution of polysulfides. Additionally, the synthesis mechanism of 3D-GS is elucidated by XPS and DFT analyses, where replacement of hydroxyl group of 3D-rGO sponge by sulfur (S8) is found to be thermodynamically favorable. As expected, 3D-GS demonstrates outstanding discharge capacity of 1080 mAh g-1 at 0.1 C-rate, and 86.2 % capacity retention even after 500 cycles at 1.0 C-rate.