Alkanethiol-modified graphene oxides (GOs) containing alkanethiol (CxGO) molecules with varying chain lengths were synthesized through click chemistry. Then, CxGO/solution-polymerized styrene butadiene rubber (CxGO/SSBR) composites with different CxGO loadings were prepared by a solution-mixing method. By combining experiment and molecular dynamics (MD) simulation, we investigated the relationship between the microstructures and properties of the CxGO/SSBR composites. Results showed that the 1-heptanethiol-modified GO (C7GO)/SSBR composite had the smallest fractional free volume and the least mobility of the polymer chains. Moreover, the 1-octadecanethiol-modified GO (C18GO)/SSBR composite displayed the largest binding energy (Ebinding). Thermal stability, gas barrier, dynamic, and static mechanical properties were improved by introducing CxGO. The long chain length of CxGO indicated that the composites had good performance. We believe that these results provide a basis for the design and fabrication of high-performance GO/SSBR composites.