Recently,　Internet　of　Things　(　IoT)　have　been　applied　widely　and　improved　the　quality　of　the　daily　life.　However,　the　lightweight　IoT　devices　can　hardly　implement　complicated　applications　since　they　usually　have　limited　computing　resource　and　just　can　execute　some　simple　computation　tasks.　Moreover,　data　transmission　and　interaction　in　IoT　is　another　crucial　issue　when　the　IoT　devices　are　deployed　at　remote　areas　without　manual　operation.　Mobile　edge　computing　(　MEC)　and　unmanned　aerial　vehicle　(　UAV)　provide　significant　solutions　to　these　problems.　In　addition,　in　order　to　ensure　the　security　and　privacy　of　data,　blockchain　has　been　attracted　great　attention　from　both　academia　and　industry.　Therefore,　an　UAV-assisted　IoT　system　integrated　with　MEC　and　blockchain　is　pro-posed.　The　optimization　problem　in　the　proposed　architecture　is　formulated　to　achieve　the　optimal　trade-off　between　energy　consumption　and　computation　latency　through　jointly　considering　computa-tion　offloading　decision,　spectrum　resource　allocation　and　computing　resource　allocation.　Consider-ing　this　complicated　optimization　problem,　the　non-convex　mixed　integer　problem　can　be　transformed　into　a　convex　problem,　and　a　distributed　algorithm　based　on　alternating　direction　multiplier　method　(　ADMM)　is　proposed.　Simulation　results　demonstrate　the　validity　of　this　scheme.