Due to the big difference between the velocities of the transmitter and the receiver, the working mode should be reasonably designed to realize high resolution and extended scene in SA-BiSAR (spaceborne/airborne bistatic synthetic aperture radar system). Based on the ratio of the beam width to the velocity, a scheme for the computation of integration time and azimuth coverage of SA-BiSAR was described. A classification of bistatic SAR(synthetic aperture radar) configurations was introduced in terms of the antenna footprints′ size and the velocities. At the same time, accurate effect of the initial footprints offset on the image performance in azimuth direction was obtained. Simulation results validate that the proposed method can be well used for footprint synchronization error analysis and SA-BiSAR system design.