In　this　paper,　the　collaborative　optimization　is　improved　to　tackle　multidisciplinary　problems　with　coupling　design　variables　within　disciplines.　The　design　variables　are　first　distinctly　classified　into　private　and　public　ones　according　to　disciplines.　A　criterion　is　then　proposed　to　judge　the　coupling　of　private　variables　with　the　public　variables.　For　the　coupling　case,　a　strategy　is　suggested　to　decouple　the　variables　before　performing,　the　collaborative　optimization.　To　demonstrate　the　effectiveness　of　the　improved　collaborative　optimization,　two　practical　optimization　problems　are　comparatively　studied　for　uncoupled　design　variables　as　well　as　coupled　ones.　It　is　shown　that　the　present　framework　can　achieve　the　better　optimal　results　as　compared　with　other　methods.　Furthermore,　the　judge　criterion　and　the　decoupling　strategy　are　also　validated.　(C)　2016　Elsevier　Ltd.　All　rights　reserved.