Abstract: In this paper, an innovative air-borne forward-looking SAR system using antenna array is studied,and three-dimensional imaging principle is analyzed. A three-dimensional imaging process is proposed forair-borne forward-looking SAR based on the image geometry and the characteristic of echo signal, and theresolutions in three dimensions are derived. Raw data of forward-looking SAR in X-band is simulated andthree-dimensional image is achieved. The imaging result is analyzed, and simulation results show that theforward-looking SAR could achieve three-dimensional imaging, and also confirm the validity of the proposedalgorithm.