Abstract: This paper studies the principle of realizing wide swath of space-borne SAR by using range Digital Beam-Forming (DBF). Then the effect of the time domain DBF processing on the amplitude and resolution of spaceborne SAR image is summarized based on the theoretical analysis and simulation. Four range DBF processing methods corresponding to scan-on-receive are explored, which are suitable for different duration of transmit signals. Simulation results show that all methods can realize wide swath signal receiving effectively in its precondition.