Abstract: Displacement time series of precise single epoch positioning imminently before the great Wenchuan earthquake on May 12, 2008, and shortly after the earthquake at 5 GPS stations of PIXI，CHDU，JYAN，NEIJ and LUZH are obtained from the double difference positioning of the BERNESE software. Through analysis on the best fit result and comparison of different results the accuracy of the single epoch solutions is discussed. The result of data processing with YANC used as a fixed station show that there were significant anomalies in 3 displacement components of NEU at LUZH station on May 9 before the earthquake, while the vertical displacements at stations of PIXI, JYAN and NEIJ, close to or near the epicenter, were quite significant within 1 hour before the earthquake, especially the vertical displacement at PIXI station,36 kmto the epicenter, accumulated to more than300 mmwithin 1 hour before the earthquake. The post seismic horizontal displacements at PIXI station were even more striking with more than400 mmdisplacement for both components, quite close to the result of more precise weekly solutions. All these changes are significantly larger than the RMS (rooted mean squares) of the single epoch positioning solutions. Though the real time single epoch positioning solutions can not be obtained at present, the result may be used as an evidence in the study on crustal movement close to or near the epicenter imminently before great earthquakes.