The low cycle performance and low Coulomb efficiency of tin-based materials confine their large–scale commercial application for lithium–ion batteries. To overcome the shortage of volume expansion of pristine tin, Sn–Co alloy/rGO composites have been successfully synthesized by chemical reduction and sintering methods. The effects of sintering temperature on the composition, structure and electrochemical properties of Sn–Co alloy/rGO composites were investigated by experimental study and first-principles calculation. The results show that Sn–Co alloys are composed of a large number of CoSn and trace CoSn2intermetallics, which are uniformly anchored on graphene nanosheets. The sintering treatment effectively improves the electrochemical performance, especially for the first Coulomb efficiency. The first charge capacity of Sn–Co alloy/rGO composites sintered at 450 °C is 675 mAh·g−1, and the corresponding Coulomb efficiency reaches 80.4%. This strategy provides a convenient approach to synthesizing tin-based materials for high-performance lithium–ion batteries.