Abstract: Cross-border mining in underground coal mines disrupts the order of coal resource development, and has huge hidden safety danger. Accurate detection of goafs caused by cross-border mining and their boundaries is extremely important for safe mining. Conventional mine transient electromagnetic detection methods are susceptible to interference from metal and electromagnetic signals in the roadway, and its detection accuracy is limited, which makes it difficult to meet the needs of accurate interpretation of goaf boundary. For the purpose of solving this problem, a drilling transient electromagnetic method and construction technology for transmitting and receiving signals in drilling is proposed to increase the proportion of anomalous signals in the measured data. As its being far away from the roadway and close to anomalous objects, the feasible domain constraints of OCCAM inversion algorithm was studied to further reduce the volume effect and achieve the fine resistivity imaging of cross-border mining goaf. Combining with the engineering practice of a coal mine in Shanxi, the practicability and effectiveness of this method for accurately detecting the scale and nature of the adjacent mines cross-border mining goaf are tested. The results show that the borehole transient electromagnetic method is an efficient combination and beneficial supplement of mine geophysics and drilling technology. The OCCAM inversion algorithm based on feasible region constraint can be effectively applied to the accurate imaging interpretation of the boundary of the cross-border mining goaf.