The trajectory for the geosynchronous synthetic aperture radar (GEO SAR) is complicated and the ship target moving combines not only translational motion but also 3-D rotate with the different state of the sea, the echo simulation of ship target in the unified coordinate system be-come a vital problem. A new method for the echo simulation in the ship coordinate system is presented. This meth-od can simulate the real geometry of satellite and earth; ship moving, as well as the rotate (yaw, pitch, roll) in dif-ferent state of the sea. The effectiveness is verified through theoretical and simulation of ISAR imaging. It is a foundation in following the imaging of the ship target for GEO SAR.