The 3D directional borehole radar system can perform 3D mapping for the surroundings of a borehole with high resolution. The detection of the distance from the borehole and the angle in relation to the magnetic North can be completed in a single borehole. The system has many advantages over the 2D borehole radar in such aspects as high resolution, rapidness and great penetrating depth. The authors deal with the working and imaging principles and technical specifications of the 3D directional borehole radar in details and, combined with field data, show its true application results.