Abstract: In order to connect relief wells with blowout wells and improve the accuracy of the target points, it is necessary to determine the borehole position of the blowout well with detection and positioning tools. However, there is currently a lack of relevant mature technology in China. In order to solve this problem, a transient electromagnetic relief well detection and positioning method is proposed in this paper based on symmetrical excitation. A calculation model for the detection distance and azimuth was derived from Maxwell’s equations, upon which a prototype of a relief-well detection and positioning tool was developed, and then tested in downhole condition. The test result showed that the maximum detection distance of this tool reached 24.0 m, with the errors of distance and azimuth less than 10% and 5°, respectively. The research indicated that the tool could accurately locate the borehole of the blowout wells and directly connect the relief wells with the blowout wells, which laid a foundation for the relief well detection, positioning and connection technology with independent intellectual property rights in China.