Geosynchronous orbit (GEO) space is an ideal place for the synthetic aperture ladar (SAL) technology because there is no atmospheric interference and no attenuation and wavefront distortion during beam transmission in it. A space-borne SAL can provide the optical image of a GEO target with ultra-diffraction-limited resolution. To realize this aim, we establish the theoretical model of space-borne SAL imaging based on optical heterodyne detection and investigate the imaging data processing methods related to the orbital parameters, using the three-dimensional coordinate relationship between the space-borne SAL and the GEO target moving along different circular orbits around the earth's core under the effect of universal gravitation. The research results show that the space-borne SAL can produce super-diffraction-limit imaging of a GEO target using the gravitational orbital motion. Besides, the changes of orbit radius, orbital plane angle and imaging position show certain influence on the processing of imagining data, reduce imaging resolution and result in the geometric deformation of the focused image. Moreover, the position near the intersection points is the best position for space-borne SAL imaging, where the distance between the space-borne SAL and the GEO target is small, and thus the geometric deformation of focused images is small and the imaging resolution is high.