Abstract: The tendency of the development of multi robot system is distributed,autonomous,coordinated and cooperative.Based on the research of a coordinated and cooperative multi robot system,the authors build up a Multi robot Cooperation Assembly System (MROCAS ) by using the hierarchy technology and the concept of multi agent.This system has such features as automatically building or decomposing of task models,fast regrouping,as well as individual intelligence and autonomous within each robot.An assembly task can be quickly completed in a complex environment with this system.