A fast algorithm of azimuth processing for spaceborne SAR, which is called SPECAN algorithm, is proposed. Comparing with general frequency algorithms, SPECAN has advantages in computation, memory and structure. SPECAN algorithm is very important for surveying real-time processing of spacehorne SAR. The structure and special problems for SPECAN algorithm used in spaceborne SAR are mainly engaged in this paper. Finally, raw data of SEASAT-A satellite is used to test the feasibility of SPECAN algorithm.