Lightweight hollow mesoporous carbon spheres (HMCSs) with large air/carbon interface in the mesoporous shell and interior void have been successfully synthesized via a polymerization-pyrolysis-etching' route. The complex permittivity of the HMCSs can be easily adjusted by carbonization temperature in the frequency range of 2-18GHz, which is in favor of designing absorbers in different frequency range. The minimum reflection loss value of -26.4dB at 6.7GHz with a thickness of 5.0mm and the maximum effective absorption bandwidth (less than -10dB) of 5.5GHz can be gained for the HC-700/paraffin composite with only 10wt% HMCSs and a thickness of 2.5mm. To enhance the magnetic loss and improve the impedance matching of the HMCSs, electroless plating methods are employed to deposit Ni and Fe nanoparticles on the HMCSs. Benefiting from the dielectric loss, magnetic loss and impedance characteristic, the new lightweight Fe/HMCSs composite with 40wt% HC-Fe shows superior microwave absorption properties. The stronger reflection loss can be obtained at all designed thicknesses, and the peak value of reflection loss is less than -20dB at each thickness of greater than 1.2mm. The minimum reflection loss reaches -49.7dB at 13.0GHz, and the effective absorption bandwidth is 4.0GHz with a thickness of 1.6mm. This research is providing a new insight in the preparation and design of lightweight microwave absorption materials.