Due　to　the　easy　deployment,　low　cost　and　high　maneuverability,　unmanned　aerial　vehicles　(UAVs)　serving　as　aerial　base　stations　can　be　efficiently　deployed　according　to　realtime　situations　for　providing　high-quality　coverage,　which　can　improve　the　communication　efficiency　and　meet　the　requirements　of　green　communications.　However,　due　to　the　finite　flight　energy,　a　single　UAV　has　limited　capability　of　providing　seamless　long-term　service　to　ground　users.　Therefore,　the　cooperation　of　multiple　drones　relying　on　sophisticated　recharging　and　reshuffling　schemes　is　necessary.　In　this　paper,　we　investigate　an　energy-　efficient　cooperation　strategy　of　multi-UAVs　for　providing　seamless　long-term　coverage,　where　the　positioning　and　the　flight　strategy　are　jointly　considered.　We　first　introduce　a　novel　UAV　power　model,　based　on　which　we　derive　the　cyclic　UAV　recharging　and　reshuffling　constraint　in　order　to　satisfy　the　seamless　long-term　coverage　requirement.　For　maximizing　the　energy-efficiency,　we　introduce　a　two-stage　joint　optimization　algorithm　for　solving　both　the　optimal　UAV　deployment　as　well　as　the　cyclic　UAV　recharging　and　reshuffling　strategy　(CRRS).　Finally,　the　efficiency　of　our　proposed　algorithm　is　shown　by　the　simulation　results.　©　2019　IEEE.