With　the　development　of　the　Internet,　the　technical　framework　that　integrates　Internet　of　Things　(IoT)　and　blockchain　has　gradually　developed.　However,　how　to　ensure　the　secure　with　balanced　performance　of　devices　becomes　a　key　issue.　In　this　article,　we　design　a　new　multistage　session　key　negotiation　protocols　for　the　Internet　of　Things-blockchain　environment　by　using　＂Agents.＂　We　transfer　bilinear　operations　to　Agents,　which　has　strong　computing　capabilities.　Based　on　this,　the　resource　of　IoT　devices　in　the　key　negotiation　process　is　reduced　without　simplifying　bilinear　pairing　compute　and　making　them　more　secure.　The　simplified　BPR　model　and　the　random　oracle　model　ID-BJM　are　used　to　test　the　security　of　requirements　in　different　stages　of　the　scheme,　furthermore,　theoretically　analyze　its　performance　overhead.　This　protocol　can　reduce　the　computing　overhead　of　IoT　devices　in　the　key　negotiation　process　under　the　premise　of　ensuring　security.