The ultrafine Cr2O3 modified carbon aerogel (Cr-CA) composites were successfully synthesized through in situ and sol-gel method as cathode material for lithium sulfur battery. The chromium doping remarkably controls structure, decreases carbon sphere size and promotes network interconnect. The nano Cr-CA composites with large pore volume and high specific surface present stronger adsorption ability and effectively immobilize polysulfides. The Cr-CA/S composite cathodes display excellent electrochemical performance with high specific capacity and long cycling stability. Especially, the Cr2-CA/S cathode with 65.9 wt% of sulfur delivers initial specific capacity of 1343 and 987 mAh g−1 at the rate of 0.2 C and 2 C, respectively. It exhibits the outstanding long-term cyclic stability with the discharge capacity of 873 mAh g−1 at 0.5 C for the 300th cycle. The excellent performance is mainly attributed to special anchoring role of Cr2O3 to polysulfides and its catalytic effect for redox reaction process. Furthermore, the adsorb energy between polysulfides and Cr2O3 and theoretic analysis by DFT definitely reveals and supports immobilizing and catalytic mechanism.