Abstract: Ground penetrating radar plays a very important role in geological exploration, military, archaeology, construction engineering and other fields. To improve the accuracy and imaging resolution of underground target detection systems and enhance the detection ability of underground linear targets, a high gain circular-polarized double-slot Vivaldi antenna is proposed for medium and shallow underground target detection. The slot part of the Vivaldi antenna is composed of different exponential lines, which makes the slot opening direction incline inward to a certain extent, and can effectively improve the gain of the antenna. Two double-slot Vivaldi antennas are combined in an orthogonal form, and are fed with equal amplitude and 90° phase difference to realize the circular polarization radiation. The simulation and measurement results show that the VSWR of the proposed is less than 2 in the range of 0.5-3 GHz. In this band, the antenna gain is greater than 3.5 dBi and the maximum gain can reach 12.5 dBi. The axial ratio in the working frequency band is less than 3 dB and the antenna has good time domain characteristics. The proposed antenna has the characteristics of ultra-wideband, high gain and circular polarization. These characteristics make the antenna proposed in this paper have broad applications in underground target detection.