Abstract:An Ms8.0 earthquake struck Wenchuan in Sichuan province on May 12th 2008 and had resulted in severe damage. On the basis of the GPS observation data from the reference stations of Crustal Movement Observational Network of China, the continuous 31day TEC values over whole China were computed, examined and compared with two statistical analysis method,both the results showed that the ionospheric TEC anomaly did exist 1-6 days prior to the earthquake in the region, the apparent anomalous reduction of TEC occurred on most of these days except the May 9th on which the TEC value anomalously increase evidently, and it was also shown that the anomalous crest of the TEC moved toward equator. Seeing the time was close to the moment when the earthquake occurred, it can be concluded that the existent ionospheric anomaly is possibly related to the earthquake after excluding all the other possible factors.