Array Synthetic Aperture Radar (ASAR) system radar imaging field has gained attention because of its three-dimensional (3-D) imaging ability. A novel Circular Array SAR (CASAR) system is employed for 3-D high-resolution radar imaging to overcome the drawbacks exhibited by linear array SAR in high-resolution imaging and by circular SAR in side-lobe suppression. Point Spread Function (PSF) model based on the CASAR system is derived, and the advantages of the new configuration of the circular array in 3-D imaging are theoretically analyzed. Prototype CASAR experimental system is built on the basis of the abovementioned analysis. PSF simulation experiments and outdoor 3-D CASAR imaging experiments under outdoor conditions are performed to verify performance of the CASAR system in 3-D SAR imaging. Compared imaging results acquired using linear array SAR, circular SAR, and CASAR system proves that the CASAR system has highresolution 3-D SAR images and demonstrates effective side-lobe suppression capability.