In this paper, an innovative airborne forward-looking SAR system using antenna array mode is studied and three-dimensional imaging principle of this system model is analyzed. A three-dimensional imaging processing method for airborne forward-looking SAR is proposed, and the resolutions in three dimensions are derived. Raw data of forward-looking SAR in L-band is simulated and three-dimensional image is achieved. The imaging result is analyzed, and simulation results show that forward-looking SAR could achieve three-dimensional image, and also confirm the validity of the proposed method.