Abstract: In recent years, resistivity observation in Yanqing station appeared with more than once remarkable anomalies caused by environmental interference, especially the iron interference on disturbance amplitude and pattern. According to underground high density electric structure profile and electrical sounding of Yanqing station, we established a three-dimensional numerical model to analyze the influence from several iron media on the amplitude and the pattern of the earth resistivity. The results showed that after deducted the reference value of earth resistivity, the disturbance amplitude and pattern tallied with the actual observed anomalies, which verified that the iron medium has interference on earth resistivity observation from the perspective of numerical analysis.