Abstract: ‍ ‍Geosynchronous synthetic aperture radar （GEO SAR） has the advantages of short revisit cycle， long dwell time and wide observation swath. It has great application value in vegetation measurements and natural disaster detection and has attracted the interest of many national researchers. At present， there is no available measured data of GEO SAR， and many of the proposed imaging algorithms take point target as the verification object， but they may not be applicable to distributed target. And in future observation scenes， they are all distributed targets. Therefore， it is necessary to simulate echo of distributed target in GEO SAR system. In the form of point target echo simulation as the foundation， in view of the problem of large amount of data and low simulation efficiency in GEO SAR， this paper proposes a fast construction scene by interpolation method， and the stop-go-stop error and azimuth window function design are considered in the echo simulation， to ensure that the echo simulation is accurate to the actual situation. Two methods of target scattering intensity design are proposed. Finally， the accuracy of echo simulation is verified by imaging.