Lithium sulfide (Li2S) is considered as an attractive cathode material for Li/S batteries due to its high theoretical specific capacity. In order to overcome its poor conductivity, Li2S is often compounded with carbon materials. However, the composites prepared by the traditional physical mixing method have low loading content, poor dispersion, large particle size of Li2S and lack of binding effects for polysulfides shuttle. Herein, we prepare nano-sized Li2S/graphene aerogel composite by in-situ lithiation of nano-S precursor. The Li2S loading in this composite is high (69.0 wt%) and variable, the nanoscaled particle size (ca. 10 nm) retains well from the elemental S precursor and disperses evenly on the three-dimensional porous graphene aerogel. More importantly, COS chemical bonding is retained between Li2S and graphene skeleton, thus the dissolution of polysulfide species and the shuttle effect can be effectively suppressed. After the lithiation process, the specific surface area is also unexpectedly increased by a factor of 10, greatly improving the lithium ion transport path, and contributing to an increase in rate performance. As a result, the in-situ lithiated Li2S/graphene aerogel composite exhibits higher specific capacity and stability compared to that via ex-situ infiltration route.