Core-shell shaped composites with tunable core compositions have been successfully synthesized by a two-step method. Initial, SnO2@C was prepared by fixing the hollow SnO2 nanospheres into the void of amorphous carbon. Followed by another annealing treatment, SnO2 was gradually reduced to metallic Sn in a mixed H-2/N-2 atmosphere and leaded to Sn/SnO2 or Sn cores. Subsequently, the original SnO2 hollow nanospheres in the core was collapsed and transformed from clusters to nanoparticles. The electromagnetic absorption properties were significant improved for the binary composite (Sn/SnO2@C) as compared to SnO2 hollow sphere, SnO2@C and Sn@C products. The effective absorption frequency width was up to 7.1 GHz with a matched thickness of 1.5 mm. The excellent electromagnetic absorption mechanism was attributed to the balanced impedance matching and attenuation ability. Besides, the existed Sn/SnO2 interface plays a key role on the attenuation intensity since the boosted interface polarization intensity.