A planar bi-directional radiation antenna including a substrate, a first reflecting element, an antenna body, a second reflecting element and a third reflecting element is provided. The first reflecting element is concaved inwards to form a first notch in a first surface. The antenna body is located inside the first notch, and is symmetrical to a predetermined direction with the first reflecting element. The second reflecting element is concaved inwards to form a second notch in a second surface. The configuration of the first notch and the second notch is correspondingly disposed along a vertical projection plane with respect to the substrate. The third reflecting element is opposite to the antenna body along the predetermined direction, and covers an opening of the first notch, so that the antenna generates two beams, wherein the two beams have an angle relative to the substrate, so as to achieve a bi-directional radiation effect.