In this paper, a simple method to prepare flexible and porous S–CNT composite film which can be directly used as the cathode for Li–S batteries is proposed. Using slightly oxidized CNT film preprepared by vacuum filtration(32, 33) as a conductive and flexible framework, thin sulfur layers having a thickness of ∼10 nm can be homogeneously coated onto the surface of each CNT. Since oxygenic groups are generated on the surface of preoxidized CNTs and a two-step heating process was involved in the experiments, the formation of strong covalent bonds between sulfur and CNTs is successfully realized. Together with the high electrical conductivity of the CNT network, the thin thickness of the sulfur layer, and the open nanopores within the film, the S–CNT composite film exhibits outstanding electrochemical performance. Moreover, the high sulfur content of 65 wt % results in high energy density of ∼1200 W h kg–1 based on the total mass of the electrode.