In view of the complex electromagnetic environment in nuclear power plants, based on the three-dimensional models of wireless gateways and wireless sensors, the TLM solver was used to analyze the electromagnetic shielding characteristics and electromagnetic sensitivity characteristics of wireless gateways and wireless sensors. By simplifying the external interference sources into uniform plane waves, the shielding effectiveness curves at the central position and the current-voltage curves at the load position of the wireless gateway and wireless sensor under the incidence of uniform plane waves were obtained. The field distribution cloud maps at resonant and non-resonant points of the wireless gateway and wireless sensor were compared. The simulation results show that under the influence of external interference sources, the wireless gateway and wireless sensor will have multiple resonant points. Near these resonant points, the shielding effectiveness is relatively low, which is not conducive to the effective shielding of the shielding chamber. Therefore, during the design process, these resonant points should be avoided as much as possible, and the overall shielding effectiveness should be improved. At the same time, in the high sensitivity area, that is, the area with the maximum induced current, the circuit’s response to the external interference source is more significant. In practical applications, wireless gateways and wireless sensors should avoid working in high sensitivity areas to reduce the impact of external interference.