Circular SAR (CSAR) is a newly developed all-directional high resolution 3D imaging working mode in recent years,to satisfy the demand of finer observation especially from different looking angles.The National Key Laboratory of Science and Technology on Microwave Imaging,Institute of Electronics,Chinese Academy of Sciences (MITL,IECAS) studies and had the first flight experiment with a P-band full polarization SAR system,and successfully obtained the all-directional high resolution Circular SAR images.Circular SAR imaging formation algorithms are firstly discussed here,which emphases on airborne experiments data processing.Then studies on the key techniques,and the development trends for this unique mode such as scattering mechanism research,3D resolution with terrain illustration and it’s application on land cover classification with polarimetric data,etc.Initial results show that CSAR technique has the encouraging potential capability in the fields of high precision mapping,disaster evaluation,resource management and the other related applications.