With　the　development　of　cloud　computing,　cloud　platforms　of　different　types　and　purposes　are　emerging.　Hybrid　clouds　are　needed　to　manage　cross-domain　computing　and　storage　resources　in　a　unified　manner　in　order　to　satisfy　management　requirements　such　as　legacy　system　integration　and　dynamic　resource　scaling.　However,　there　are　differences　in　management　interfaces　and　mechanism　between　different　cloud　platforms,　which　cause　great　difficulties　and　high　complexity　to　construction　of　hybrid　clouds.　In　this　paper,　a　runtime　model　based　approach　to　managing　hybrid　clouds　is　presented.　First,　the　manageability　of　cloud　platforms　is　abstracted　as　runtime　models　based　on　their　management　interfaces.　Second,　a　unified　model　of　cloud　software　architecture　is　provided　according　to　the　domain　knowledge　of　current　cloud　platforms.　Third,　the　synchronization　between　the　unified　model　and　cloud　runtime　models　is　ensured　through　model　transformation.　Thus,　all　the　management　logic　can　be　carried　out　by　executing　programs　on　the　unified　model,　which　decreases　the　difficulty　and　complexity　of　hybrid　cloud　construction.　The　experiment　on　a　real-world　hybrid　cloud,　which　consists　of　CloudStack　and　Amazon　EC2,　demonstrates　the　feasibility,　effectiveness　and　benefits　of　the　new　approach　in　managing　hybrid　clouds.　©　Copyright　2017,　Institute　of　Software,　the　Chinese　Academy　of　Sciences.　All　rights　reserved.