The invention relates o a C/X dual-wave waveband shared aperture waveguide slot array antenna, which is mainly applied to a multi-functional and multi-purpose composite radar. The antenna comprises an X waveband waveguide slot antenna, a radiation transition cavity and a C waveband waveguide slot antenna, wherein the X waveband waveguide slot antenna adopts a waveguide narrow-side inclined slot radiating unit; the C waveband waveguide slot antenna adopts a waveguide wide-side slot radiation array antenna. The working frequency difference of the two antennae is used, the C waveband waveguide slot antenna is placed behind the X waveband waveguide slot antenna, impedance matching from the C waveband waveguide slot antenna to an X waveband antenna linear array slot is realized by using the radiation transition cavity, and electromagnetic wave radiation of the C waveband waveguide slot antenna is realized through the linear array slot.