A dual-band shared-aperture antenna array based on a dual-mode parallel waveguide is applicable to the field of wireless communications technologies. The dual-band shared-aperture antenna array includes: a waveguide-substrate integrated waveguide transition structure, a multi-stage cascaded power splitter, a transverse coupling slot, a longitudinal coupling slot, a matching through-hole, a shared-aperture dual-mode parallel waveguide, and a shared-aperture parallel slot array. The entire structure includes two dielectric substrates. A signal is input to the multi-stage cascaded power splitter through the waveguide-substrate integrated waveguide transition structure located on a bottom-layer substrate. The foregoing dual-band shared-aperture antenna array based on a dual-mode parallel waveguide can separately implement a low-band fixed-beam slot array antenna, a high-band multi-beam long slot leaky-wave antenna, or a fixed-beam slot array antenna. It has a simple structure, multiple functions, high integration, a small size and light weight.