The paper proposes a miniaturized, high-gain, ultra-wideband and end-fire antenna which covers 2.7～18.3 GHz band to overcome the large size and small forward gain at low frequency of conventional Vivaldi antenna. By adding Y-shaped apertures on both sides of the radiation patch, the surface current of antenna converges near the through line，so the radiation property is improved, including the impedance bandwidth, the antenna gain and the end-fire effect. The size of the antenna is only 25 mm×25 mm×1 mm, thus achieving a significant miniaturization. The gain of low frequency part (2.7～8 GHz) is increased to a maximum value of 3.5 dB compared with the original antenna. The test result of the fabricated antenna demonstrates the reliability of the design.