The　cooperation　between　two　master-slave　modular　robots　is　studied　in　the　paper.　A　cooperative　robot　system　is　set　up　with　two　modular　robots　and　a　dynamic　optical　meter-OptoTrak.　With　OptoTrak,　the　position　of　the　end　actuators　is　measured　as　the　optical　position　feedback,　which　is　used　to　adjust　the　actual　robots　end　positions.　A　tri-layered　motion　controller　is　designed　for　the　two　cooperative　robots.　With　the　kinematics　constraints　of　the　two　robots　including　position　and　pose,　joint　velocity　and　acceleration　constraints,　the　two　robots　can　cooperate　well.　A　bolt　and　screw　assembly　experiment　is　executed　to　verify　the　methods.　©　2009　IEEE.