S-doped mesoporous graphene microspheres (SMGMs) derived from the chemical vapor deposition process, are employed as reservoir materials for LiS batteries. A steam-impregnation process is applied to fabricate a S@SMGMs composite with homogeneous distribution of sublimed S in the graphene matrix. The S@SMGMs cathode prepared by the steam-impregnation process exhibits higher capacity (830 mAh g−1 at 8 C) and better rate capability as compared to the cathode obtained from the conventional melt-diffusion process. Good structural integrity of the S@SMGMs composite is well kept after cycling. The outstanding electrochemical properties of the S@SMGMs composite cathode are mainly benefited from the perfect compounding-state between graphene and S, the unique microarchitecture decorated with highly stable porous structure and S doping. Additionally, the contribution of S doping to constraining Li-polysulfides is further confirmed by density functional theory calculations, which indicates that the binding energies between Li-polysulfides and oxided S are higher than that of thiophene-S.