On August 8, 2017, an Ms 7.0 earthquake hit Jiuzhaigou County, Sichuan Province, China. Before the earthquake, the AETA system was equipped with 6 monitoring stations in Jiuzhaigou County, Songpan County, Pingwu County, Qingchuan County, Maoxian County and Wenchuan County of Sichuan Province within a 200 km radius of the epicenter. With sliding principal component analysis (PCA) method, whose length of time window is 30 days, we analyzed the characteristics of electromagnetic disturbance of these six stations, and discussed the coand post-seismic changes of the electromagnetic field observed by the AETA system, and proposed a new impending seismic feature, namely the “anomaly band”. The results show that except the day of Jiuzhaigou Ms 7.0 earthquake, anomalous points appeared on monitoring station of Jiuzhaigou in the same period (5:00 am–6: 00 am) from the 5th day before the earthquake to the 15th day after the earthquake, and the anomalous value generally presented the trend of increase before the earthquake and decrease after the earthquake. Although anomalous points appeared on other monitoring stations, these points were scattered and the anomaly value was low. Within Two months after the abnormal band disappeared, there were no obvious band anomaly and no strong earthquakes.