In order to reduce the threat of radar detection to stealth equipment such as missiles, aircraft and ships, an ultra-wideband (UWB) high gain Vivaldi antenna with low radar cross section (RCS) was designed. By analyzing the surface current distributions of the antenna at different frequencies, a simple and effective method is adopted to change the shape of the antenna without affecting the radiation performance of the antenna, and a rectangular and semicircular shaped structure is loaded on both sides of the radiation arm. The proposed structure can reduce the scattering on the surface of the radiator, leading to the monostatic RCS reduction. The measurement results show that the proposed antenna has a working bandwidth of 4. 7~ 11 GHz and a maximum gain of 11 dBi. Compared with the original antenna, the proposed antenna maintains good radiation performance. At the same time, the maximum reduction of RCS is 18. 5 dB in the working frequency range. The proposed antenna can be applied to stealth systems with low RCS.