We propose a broadband artificial magnetic conductor (AMC) composite structure for reducing radar cross section (RCS). By combining multiple periodic metal square patches together, we further broaden the working bandwidth of the AMC composite structure. The tested results indicate that the reflection is below -10 dB in a frequency range of 7.7—13.1 GHz, and the relative bandwidth is 51.9%. We study the scattering characteristics of the AMC composite structure at different frequencies by full wave simulation. Reflection peaks in the opposite quadrant bisector of plane shift close to the normal direction with the increase of frequency, but the backscattering RCS of the AMC composite structure is still about -8 dB smaller than that of the metal plate. The AMC composite structure has the advantages of broad working bandwidth, simple design, easy processing, etc, and has important application foreground.