Flexible DC transmission systems are widely used in long-distance power transmission, renewable energy integration, and urban grid interconnection. As a core power device in these systems, the performance of the IGBT directly affects the reliability and efficiency of the entire system. Therefore, detecting the chip health status of the Press Pack-Insulated Gate without compromising its inherent packaging is of significant importance for improving the stable operation of power systems. This paper first analyzes the internal structure and magnetic field distribution characteristics of the Press Pack-Insulated Gate. During operation, the internal current generates a specific magnetic field distribution, which is closely related to the device’s health status. By monitoring changes in the external magnetic field, the internal current distribution can be indirectly inferred, thereby assessing the device’s health status. However, due to the presence of significant external magnetic interference, it is challenging to directly measure the external magnetic field to reconstruct the current distribution. To address this issue, this paper proposes a method to significantly reduce external magnetic interference by optimizing the placement and orientation of sensors, thereby accurately capturing the internal magnetic field characteristics of the Press Pack-Insulated Gate. Finally, the effectiveness of this method is validated through experimental simulations. The simulation results show that by optimizing the sensor placement, external magnetic interference is significantly reduced, and the monitoring accuracy of the magnetic field characteristics is greatly improved.