Different from common “Metamaterials”, “Metacomposites” are used to describe random nanocomposites with negative permittivity, which is determined by controlling their microstructures and compositions. Metacomposites with unique negative permittivity show potential applications in superconductors, wave filters, capacitors, electromagnetic interference shielding or absorbing and other fields. In this review, Drude model, Lorentz model and “double nano wires” model used to analyze negative permittivity were discussed. Preparation, properties and mechanism of negative permittivity from metacomposites in corporation of carbon nanomaterials as fillers were reviewed and analyzed. Besides, the applications of metacomposites in the field of electromagnetic wave absorption and improving the performance of the antenna were also discussed.