Abstract: Take the advantage of all-directional observation of circular SAR, an approach of the outlines extraction of building footprints from the circular SAR data is presented, while the approach can also be used for estimating the ground altitude around the building. The proposed approach is as follows: firstly, the rough altitude of the ground around the building is estimated by radargrammetric Digital Elevation Model (DEM) extraction, secondly, image planes are set in certain range where the estimated altitude is in the middle, and circular SAR image of the building is obtained on each image plane. Finally, one image is selected where a closed polygon frame is formed by the double bounce scattering bright lines from the building, and the outlines of building footprints are extracted from the image, while the altitude corresponding to the imaging plane is defined as the altitude of the ground around the target building. The proposed method is validated by the circular SAR data processing by the experimental SAR airborne system at P bands.