The earthquake frequency field is a mathematical method to describe the temporal and spatial characteristics of seismic frequency. Taking the area near the epicenter of Wenchuan M_S8.0 earthquake on May 12, 2008 (30.0°-33.0°N, 101.5°-105.5°E) as the research area, the time variation characteristics of typical field time factors of frequency field were analyzed with the expansion method of natural orthogonal function. When the typical fields corresponding to the first eight eigenvalues were taken, the fitting accuracy reached 0.936 8, and six typical fields showed abnormal changes, accounting for 0.691 1 of the total field. The anomaly occurred in September 2004 at the earliest, that is, 3 years and 7 months before the main shock, and more than 1 month before the main shock at the latest, showing the characteristics of short-term and imminent anomaly. The results showed that the seismic frequency field method can ideally extract the anomalies before the Wenchuan M_S8.0 earthquake.