A new method to visualize the coupling path is proposed to help solve electromagnetic compatibility problems. By using the reciprocity theorem and the concept of reaction, the coupling density coefficient (CC) is defined. Integration of the CC on closed surfaces equals the coupled power at the receiver. By plotting the CC on a set of surfaces from the source to the receiver, the coupling path, which traces the coupled power flow, can be visualized. All visualization procedures can be performed in a full-wave simulation tool, thus making the proposed method convenient to use. To validate and demonstrate the potential benefits of the new method, visualization of the coupling path in a realistic automotive intentional electromagnetic interference problem is presented. In addition, a mitigation solution based on the visualization result was examined.