The cancellation of the antenna mode scattering field of the dummy elements and the structure mode scattering field of the whole array is proposed, which is used to reduce the radar cross section(RCS) within the antenna band. Only the amplitude and the phase of the antenna mode scattering field of the dummy elements are controlled, so that the radiation properties of the array antenna are remained. The structural mode scattering field and antenna mode scattering field of Vivaldi antenna element and multi element arrays are studied. The affection of impendence loads on the antenna mode scattering field of dummy element is analyzed. The Vivaldi array with a configuration of 1×6 is designed, and the in-band dual-polarization RCS reduction is achieved by regulating the load impendence of the dummy element. When the electromagnetic waves are incident in the normal direction, the co-polarization RCS reduction is achieved in the frequency band of 6.7-8.9GHz, and the reduction peak reaches 14.9dB. Cross-polarization RCS reduction is achieved within the 8.3-12GHz frequency band, with a reduction peak of 17dB. On the 30° oblique incident condition, the co-polarization RCS reduction was achieved within 6.7-10GHz frequency band, with the reduction peak reaching 23.5dB. This method reduces the dual-linear polarization RCS within the antenna operating frequency band without changing the structure of antenna, which has good engineering application value.