Abstract: ENVISAT ASAR images were used to measure coseismic displacement field of the 2008 Wenchuan earthquake in both the line of sight and azimuth directions of the sensor. Cross-correlation method was utilized to match the images before and after the earthquake in precision of sub-pixel level. And then we analyzed surface rupture geometry and motion feature of the Longmenshan fault zone. Two large scale surface ruptures are identified on the map. One is distributed along Beichuan-Yingxiu fault, about 230 km long. And the other is distributed along Guanxian-Jiangyou fault, about 65 km long. The two deformation maps also illuminate motion characteristc of the Longmenshan fault zone. The southwest part of Beichuan-Yingxiu fault is characterized by thrust dominant motion, while the northeast part shows right-lateral slip.The Guanxian-Jiangyou fault is a thrust-dominant fault. This result is in well accordance with InSAR/GPS and field surveys and reveals coseismic displacement features of the Wenchuan earthquake from a new sight.So sub-pixel matching method， together with other methods，will serve as an effective technique in the research of surface ruptures and fault activity.