Range-Doppler algorithm can be applied to imaging of spaceborne bistatic SAR. Range models used by the algorithm include quadratic model and beeline model. Considering the bistatic character of the system, method of getting precise range model parameters was studied. RD algorithm was deduced using quadratic model. In squint side-looking situation, quadratic model may have inignorable error. The error mainly can influence azimuth compression. In order to suppress azimuth sidelobe, imaging using azimuth compressing function according to beeline model was studied. For preserving image phase, right azimuth compressing function should be used to avoid destruction of the phase.