Abstract: On 12 May 2008,a Mw 7.9 Wenchuan Earthquake occurred in Sichuan Province,China,which is located in Longmenshan mountain area with bald relief and dense vegetation.The smaller wavelength(C-band) system can not provide high quality interferograms.In order to map co-seismic deformation in earthquake region,the SAR data collected by L band ALOS/PALSAR sensor of JAXA are used in the study,including before and after the quake from six paths.A two-pass differential InSAR technology and external DEM acquired by SRTM mission are employed in GAMMA software to generate the co-seismic deformation field.GPS observation results of co-seismic deformation surveyed by Chinese national large scientific project-Crustal Movement Observation Network of China(CMONC) project team are used to evaluate the InSAR observations.The result shows that there is a high consistent between GPS and InSAR observations.And accuracy of line of sight surface displacement derived from traditional InSAR technique can achieve cm-level.