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This paper tries to take a retrospective analysis on the electromagnetic anomalies recorded by fixed stations prior to the 2008 Wenchuan MS8.0 earthquake, and to further understand these anomalies during the seismogenic process. There were eight georesistivity stations around the epicenter exhibiting different types of abnormal changes before the main shock. Combining analysis on the successive data after the shock, only the anomalies of Chengdu and Jiangyou stations, which are located near the rupture zone, can be explained by the existing geo-resistivity anomaly mechanism companying the seismogenic process. Two north-south geomagnetic vertical component minimum point shift lines appeared on April 24 and May 9, 2008, respectively, which are distributed approximately along the north-south seismic belt where the Wenchuan earthquake occurred. Some parameters extracted from geomagnetic data of the Chengdu station showed abnormal variations, including the transfer function, harmonic amplitude ratio, Parkinson vector, and vertical polarization intensity, which mainly reflect the underground conductivities. The geoelectric field and electromagnetic data near the rupture zone displayed phenomena of waveform distortion and energy enhancement. The geoelectric field recorded at the Xichang geoelectric monitoring array and Tianzhu-Songshan monitoring array also showed phenomena of power spectrum energy increases and disturbances of the fracture water penetration direction calculated from the geoelectric field data. Three stations in the Hebei electromagnetic monitor network, which was more than 1 300 km far from the epicenter in NE direction to the Longmenshan fault, recorded the most obvious abnormal variations a few months before the earthquake since the 1980s.
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