Abstract: Orientated borehole ground penetrating radar (OBGPR) can effectively solve the problem of orientated and detailed detection of geological conditions around the mine or oil well boreholes and engineering probe hole, etc. In view of difficult state control and unsatisfactory detection effect during antenna sagging due to the changeable medium in deep hole and the unreasonable counterweight of OBGPR antenna, the balance analysis and counterweight optimization design of orientated borehole ground penetrating radar antenna during detection was implemented in this paper. Firstly, analysis was conducted on the force of OBGPR antenna under the balance condition during the deep hole and well detection. Definitely, the model of viscosity coefficient of drilling mud changing with density was built under the condition of the known gravity and buoyancy of antenna in medium with different densities. On this basis, the relationship between Reynolds number and drag coefficient was obtained through numerical simulation and experimental verification. In particular, the movement resistance of OBGPR’s antenna for detection at uniform velocity was studied. Then, the counterweight optimization design was operated for OBGPR antenna, forming the adjustable counterweight structure and the counterweight schemes under different detection conditions (with borehole diameter of 0.1‒0.2 m, medium density of 1 000‒1 700 kg/m³ and detection speed 0.3‒0.6 m/s). Besides, the field detection tests were carried out for the quality of pylons and dam foundation of OBGPR, to verify the counterweight optimization design result of antenna. Moreover, analysis was performed for the change of cable tension and the detection results of radar. The results show that the optimized counterweight structure and scheme of OBGPR antenna could meet the detection requirements of antenna under different conditions, and according to the detection results, the orientation and size of the geological anomaly area around the borehole could be obtained accurately. Generally, the research results could provide technical support and guidance value for the borehole ground penetrating radar to realize the ultra-deep, orientated and detailed detection in complex borehole/well environment.