The invention discloses a knife-shaped dual-frequency horizontal polarization omnidirectional antenna. The antenna comprises an antenna cover and an antenna; the antenna is packaged in the antenna cover; the antenna comprises an antenna radiation unit and a feed unit; the antenna radiation unit is a cuboid with an opening in an aperture surface; the aperture surface with the opening is named as an opening surface; the feed unit is positioned in the antenna radiation unit, and positioned in the center in a perpendicular direction; the feed unit is a metal patch in a gradually changing form; a U-shaped groove is formed in the metal patch in the gradually changing form. The antenna is simple and creative in structure, relatively small in size, stable in directional diagram, good in omnidirectional performance, low in cross polarization, and capable of realizing controllable frequency dual-frequency resonance characteristic, high gain and the like; and the knife-shaped dual-frequency horizontal polarization omnidirectional antenna is applicable to the field of the mobile communication.