Abstract: In order to study microwave absorbing properties of composites reinforced by irregular carbon fiber , the surface topography，microstructure and chemical composition of irregular carbon fiber (ICF) and T300 were investigated by scanning electron microscopy (SEM)，X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results indicate that the cross-section of the irregular carbon fiber is approximately regular triangle，the degree of profile is 13.16 %，and the interaction with resin matrix is strong. The mechanical property of ICF is comparative to that of T300，and ICF can be used as structural materials. The electromagnetic property and microwave absorbing property of the composites reinforced by ICF and T300 were also analyzed by four-probe measurement，mesh method and radar cross section (RCS). The results show that the resistivity of the composites reinforced by ICF is larger than that of composites reinforced by T300. For high frequency electromagnetic wave，both the imaginary part of permittivity (ε″) and loss tangent (tanδ) of the composites reinforced by ICF are higher than those of composites reinforced by T300. For electromagnetic wave with frequency about 16 GHz，the reflectivity of the composites reinforced by ICF is - 8dB. According to the test results，the composites reinforced by ICF have both the function of load bearing and the electromagnetic energy absorbing capability，and the composites as radar absorbing structure (RAS) will become a promising material .