Abstract: In Bistatic spotlight SAR design,azimuth resolution is a key factor.The theoretical analysis in this paper is based on the space geometry model,the transmitter and receiver fly on different platforms and at different height,two flight paths are parallel.Then demonstrate the equation of the azimuth resolution of the Air-born bistatic spotlight synthetic aperture radar.After the simulation and the theoretical analysis of the system,the influence of different initial conditions is discussed on the system azimuth resolution.The simulation results indicate that the azimuth resolution is determined not only by radar wavelength,LOS angle,but also by the position of transmitter and receiver.