This paper presents the image technique and the moment method (MM) for analyzing electric field distributions inside a metallic house, located under 345 kV power transmission lines. The validity of the numerical method is checked by comparing it with the experimental results of the electric fields measured inside the metallic house. Results showed that the validity of the numerical method is extremely accurate. In the future, electric fields induced inside houses located under power transmission lines can be accurately calculated by using the MM technique in the place of time‐consuming measurements.