Herein, we successfully constructed a Cu+-doped PVA-derived mesoporous carbon@diatomite (DE) composite by virtue of N2-suffered carbonization and self-reduction at a high temperature. The structure and composition of C/Cu@DE composite adsorbents were determined by a series of characterizations. The results affirmed that Cu+ species are highly scattered in PVA-derived mesoporous carbon, which covered the DE surface. The effect of carbonization temperature on the structure and composition of the C/Cu@DE composite adsorbents were intensively investigated, indicating that the C/Cu@DE composite at an 800 °C carbonization temperature (C/Cu@DE-800 °C) showed the formation of many Cu+ species and preferable hierarchical pore properties. The adsorption experiments of benzothiophene (BT) indicated that C/Cu@DE-800 °C possessed a better adsorption capacity. The adsorption behavior of BT onto C/Cu@DE-800 °C was investigated by a variety of adsorption times, initial concentrations, and recycle times, of which the largest adsorption capacity for BT attained 34.2 mg/g. Furthermore, the adsorption kinetics, intraparticle diffusion, adsorption isotherms, and adsorption thermodynamics of BT onto C/Cu@DE-800 °C was deeply studied, which contributed to the proposed adsorption mechanism.