With　the　rapid　development　of　Internet　of　Things　(IoT),　more　and　more　applications　focus　on　the　detection　of　unmanned　areas.　With　the　assistance　of　unmanned　aerial　vehicle　(UAV),　IoT　devices　are　able　to　access　the　network　via　aerial　base　stations.　These　UAV-assisted　IoT　applications　still　face　security　and　energy　challenges.　The　open　environment　of　IoT　applications　makes　the　application　easy　to　encounter　external　invasion.　Limited　energy　of　UAV　results　in　the　limited　lifetime　of　network　access.　To　address　these　challenges,　researches　on　IoT　security　and　energy　efficiency　are　becoming　hotspots.　Nevertheless,　in　the　UAV　continuous　coverage　scenario,　there　is　still　an　enormous　potential　to　improve　the　security　and　efficiency　of　data　collection　in　IoT　applications.　In　this　article,　blockchain　is　introduced　into　the　scene　of　UAV-assisted　IoT,　and　a　data　collection　system　considering　security　and　energy　efficiency　is　proposed.　In　this　system,　UAV,　as　an　edge　data　collection　node,　provides　a　long-term　network　access　for　IoT　devices　through　regular　cruises　with　recharging.　By　forwarding　data　and　recording　transactions,　UAVs　get　charging　coins　as　rewards.　UAVs　use　charging　coins　to　exchange　charging　time.　UAV　swarm　builds　distributed　ledgers　based　on　blockchain　to　resist　the　invasion　of　malicious　UAV.　In　order　to　reduce　energy　consumption,　this　article　designs　an　adaptive　linear　prediction　algorithm.　Through　this　algorithm,　IoT　devices　upload　prediction　model　instead　of　original　data　to　greatly　reduce　in-network　transmissions.　Simulation　results　show　that　the　proposed　system　can　effectively　improve　the　security　and　efficiency　of　data　collection.　©　2014　IEEE.