GEO synchronous Synthetic Aperture Radar(GEO SAR) formation means that two or more GEO satellites which carry SAR system working together and form a large virtual satellite to finish more tasks and reduce the risk. There are several channels in GEO SAR formation, which can be utilized to detect the moving target. Space-Time Adaptive Processing(STAP) suppresses clutter in space-time plane to accomplish moving target detection in the background of strong clutter. According to the traditional STAP algorithm, this paper proposes a method of moving target detection based on the GEO SAR formation and analyzes the performance through the simulation.