Functionalized porous carbons are necessary for the reversible operation of lithium-sulfur batteries (LSBs), however, their appropriate utilization and physicochemical states in the sulfur cathode are still unclear. Although numerous studies regarding distribution of sulfur in the pores of the carbon framework in the cathode have been reported, sulfur distribution and oxygen coverage on the carbon surface after sulfur infiltration have not been clearly investigated. In this study, we scrutinized the role of the pores in the oxygen-functionalized mesoporous carbon nanoparticle (O-MCN). Furthermore, we elaborated sulfur distribution, oxygen coverage, and pore utilization of O-MCN under the three different sulfur infiltration process. The soft x-ray scanning transmission x-ray microscopy (STXM) was used for the first time in the LSB system. The STXM enabled probing of local distribution of sulfur and the chemical nature of sulfur and oxygen in O-MCNs. Our findings provide a comprehensive understanding about how the sulfur infiltration process impacts the sulfur utilization during the redox reaction of sulfur in the oxygen-functionalized mesoporous carbon.