The　design　of　high-performance　compounded　flame　retardants　based　on　multielement　can　be　of　great　significance　for　reducing　the　flammability　of　polymer　materials.　In　this　article,　a　new　type　of　N-P-Cu　containing　supermolecular　assembly　network　(MPCSN)　flame　retardant　was　prepared　and　subsequently　added　into　thermoplastic　polyurethane　elastomer　(TPU)/silicon　microencapsulated　ammonium　polyphosphate　(SiAPP)　composites.　The　obtained　results　indicated　that　a　series　of　TPU/SiAPP/MPCSN　composites　exhibited　strong　adhesions　with　the　TPU　matrix.　Additionally,　the　thermal　and　flame　retardant　performances　of　TPU　composites　were　markedly　improved　after　the　introduction　of　different　proportions　of　SiAPP　to　MPCSN.　For　example,　the　peak　of　heat　release　rate,　the　total　heat　release,　the　peak　of　smoke　production　rate,　the　total　smoke　release　of　the　TPU　composite　containing　7.5 wt%　SiAPP　and　2.5 wt%　MPCSN　(TPU/SiAPP3/MPCSN1)　remarkably　decreased　by　68.7%,　52.9%,　52.4%,　and　49.4%,　respectively,　besides　the　highest　LOI　value　(27.5 vol%)　and　UL-94　V-0　rating,　compared　with　those　of　pure　TPU.　The　improved　flame　retardance　of　the　TPU/SiAPP3/MPCSN1　composite　was　due　to　the　explanations:　On　one　hand,　a　compact　intumescent　char　effectively　protected　the　TPU　matrix　from　heat　and　oxygen　and　retarded　the　gaseous　products　permeation　into　the　combustion　zone;　on　the　other　hand,　evolved　phosphorus-containing　free　radicals　captured　the　H•　and　HO•　generated　from　the　TPU　material.　The　synergistic　effect　of　SiAPP　and　MPCSN　resulted　in　strong　flame　suppression,　accompanied　by　10.8%　and　37.8%　reductions　in　FIGRA　and　Av-EHC,　respectively.　This　article　offers　a　facile　approach　to　fabricate　highly　effective　flame-retardant　TPU　composites.　©　2021　John　Wiley　&　Sons　Ltd.