The invention relates to a method for preparing carbon nano tube / polyaniline nano particles having metamaterial performances. A metamaterial is a new academic word arising in the physics field in this century and has an artificial composite structure having supernormal physical properties which a natural medium does not have, and the metamaterial has a negative dielectric constant and a negative permeability. The dielectric constant of the prepared carbon nano tube / polyaniline nano particles is within a range of 1 MHz to 1 GHz, the dielectric constant epsilon is -2.5*10<5>--10, the permeability mu is 1--0.005, and now there is no report that a directly prepared polymer composite has metamaterial performances. The metamaterial is prepared through material synthesis, and the application of the metamaterial to the fields of stealth, micro antennas and electronic components is expanded. The prepared carbon nano tube / polyaniline nano particles are in a powder shape, and the particle size is uniform. The method can be used for preparing the nano composite electromagnetic metamaterials.