The invention belongs to the technical field of antennas, and discloses a millimeter-wave radar single-ridge waveguide slot array antenna. The antenna comprises a dielectric plate, a microstrip line,an irregular impedance conversion band, a stepped microstrip line-to-single-ridge waveguide interconnection structure, a metallized via hole in the dielectric plate, a single-ridge waveguide, an on-ridge slot and a short-circuit end, wherein the microstrip line feed network printed on the dielectric plate feeds the antenna; the microstrip line, the irregular impedance conversion band and the stepped microstrip line-to-single ridge waveguide interconnection structure realize a switching structure with a broad band and low loss; the single-ridge waveguide, the on-ridge slot and the short-circuitend form a radiation structure with a low sidelobe and a high scanning angle; the lower layer of the dielectric plate is coated with an aluminum foil, and the upper layer is coated with a copper foilwhich serves as the lower wall of the single-ridge waveguide; and the slot is excited to produce different resonance amplitudes by alternately changing the depths of the grooves in the two sides of the upper ridge of the single-ridge waveguide. The antenna has the remarkable advantages of being easy to integrate, low in cost, easy to machine, high in efficiency, low in side lobe, wide in scanningangle, low in profile and the like.