Abstract: Electrically conducting polyaniline（PANI）-magnetic oxide（Fe₃O₄）composites with electrical and ferromagnetic behaviors were synthesized by the way of emulsion polymerization in the presence of dodecyl benzene sulfonic acid（DBSA）as a suffactant and dopant and ammonium persulfate（APS）as the oxidant.The average diameter of the composites is about 120nm.The effects of the contents of Fe₃O₄,DBSA and APS in the polymerization on the electromagnetic parameters（ε″,ε′,μ′andμ″）were studied by the permittivity and permeability measurements in the range of 2-18GHz.The results show that Fe₃O₄ can improve the magnetic and dielectric loss of the composites in a wide frequency range,theμ″andε″have increased to 0.72 and 9.62 respectively.In order to design the multilayer gradient absorbing structure,the contents of Fe₃O₄,DBSA and APS can he adjusted to influence the permittivity and permeability of the composites.As a result,the FGM can be content with the impedance matching and absorb the microwave maximumly.