In this paper, we discuss about multiple coordinated robots that can form a fixtureless manufacturing cell. It is very important to ensure that the system stiffness is sufficient for manufacturing operations when external forces are exerted on the system. For this reason, a method is developed to model and analyze the stiffness of a multiple coordinated robot system. In this paper, first, the stiffness of a multiple coordinated robot system is defined. Similar to a single-arm robot, this definition provides us with a criterion to evaluate the stiffness performance of the entire multiple robot system. Second, a static stiffness model is derived including joint stiffness and link stiffness, and then this model is extended to a multiple robot system. Third, the coordinated static stiffness model is validated, and a comparison is made through simulation between a dual robot system and a single robot system. Finally, the developed model is applied to a real coordinated dual-arm robot system for validation.