There is provided a waveguide horn array, a method for forming the waveguide horn array, and an antenna system. The array includes a rectangular metal plate which is processed to have a cross section comprised of a plurality of rectangular holes arranged in the length direction of the rectangular metal plate, the lower part of each hole being formed as a rectangular waveguide, and the upper part of each hole being formed as a horn; and a groove extending in the direction along which the plurality of holes are arranged and having a predetermined depth, which is formed at two sides of the holes on the top surface of the rectangular metal plate. According to the embodiments, it is possible to maintain the good properties of the antenna in terms of bandwidth and directivity, while enhancing the isolation between the transmitting antenna and the receiving antenna in the system.