Abstract: In this paper, the theoretical analyses and simulations of the SAR imaging processing are firstly made, the time-domain sub-aperture algorithm which is used to implement missile-borne SAR, are researched and the whole flow of the algorithm are given. Finally, thinking over the need of the practice system, a hardware system using the high performance DSP chip named TS203 to process digital signal practically are designed and the result of imaging are given. The result validates the efficiency of the time-domain sub-aperture algorithm and hardware platform.