Recently,　the　Internet　of　Things　(IoT)　has　been　applied　widely　to　provide　technical　power　for　the　rapid　development　of　the　world.　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.　Fortunately,　mobile　edge　computing　(MEC)　and　unmanned　aerial　vehicle　(UAV)　provide　solutions　to　these　problems.　In　addition,　blockchain　is　considered　and　introduced　to　realize　data　sharing　and　ensure　data　security.　Therefore,　in　this　article,　we　propose　an　UAV-assisted　IoT　system　integrated　with　MEC　and　blockchain,　and　formulate　the　optimization　problem　in　the　proposed　architecture　to　avoid　excessive　consumption　of　energy　and　computation　latency　through　jointly　considering　computation　offloading　decision,　spectrum　resource　allocation　and　computing　resource　allocation.　Considering　this　complicated　optimization　problem,　a　convex　problem　which　is　transformed　from　the　non-convex　mixed　integer　problem　is　obtained,　and　then　a　distributed　algorithm　based　on　alternating　direction　method　of　multipliers　(ADMM)　is　proposed.　Simulation　results　demonstrate　that　the　validity　of　this　scheme　which　reduce　the　energy　consumption　and　computation　latency　of　the　system　effectively,　and　improve　the　system　performance　significantly.　©　2021　IEEE.