Internet　of　Things　(IoT)　equipment　is　usually　in　a　harsh　environment,　and　its　security　has　always　been　a　widely　concerned　issue.　Node　identity　authentication　is　an　important　means　to　ensure　its　security.　Traditional　IoT　identity　authentication　protocols　usually　rely　on　trusted　third　parties.　However,　many　IoT　environments　do　not　allow　such　conditions,　and　are　prone　to　single　point　failure.　Blockchain　technology　with　decentralization　features　provides　a　new　solution　for　distributed　IoT　system.　In　this　paper,　a　blockchain　based　multi-WSN　authentication　scheme　for　IoT　is　proposed.　The　nodes　of　IoT　are　divided　into　base　stations,　cluster　head　nodes　and　ordinary　nodes　according　to　their　capability　differences,　which　are　formed　to　a　hierarchical　network.　A　blockchain　network　is　constructed　among　different　types　of　nodes　to　form　a　hybrid　blockchain　model,　including　local　chain　and　public　chain.　In　this　hybrid　model,　nodes　identity　mutual　authentication　in　various　communication　scenarios　is　realized,　ordinary　node　identity　authentication　operation　is　accomplished　by　local　blockchain,　and　cluster　head　node　identity　authentication　are　realized　in　public　blockchain.　The　analysis　of　security　and　performance　shows　that　the　scheme　has　comprehensive　security　and　better　performance.