We use the natural orthogonal function(or the empirical orthogonal function)expansion method to analyze the seismic activity energy as the random field. The calculation unit is annular,and some earthquakes with magnitude 7.0 and magnitude 6.0 have been selected as the samples. The time factor curves of the typical seismicity field in the annular zone before these magnitude 7.0 and magnitude 6.0 earthquakes have been calculated. The results have showed that the time factor curves of the typical seismicity field in the annular belt before the earthquake samples selected with magnitude 7.0 and magnitude 6.0 are obviously deviated from the normal variation. Most of the anomalies occur in 3 years before the earthquake to the imminent earthquake. The analytical method of the seismic activity field in the annular zone can also be used to analyze the spatial distribution of anomalies. Finally,the related problems about the application effect,the selection of parameters and the application in actual earthquake prediction of seismic activity field analysis method in the annular zone have been discussed.