Under　the　Mises　yield　condition,　the　failure　mechanism　of　the　adhesive　layer　between　self-compacting　concrete　and　old　concrete　is　presented　in　this　paper.　After　the　plastic　limit　analysis　of　bonding　strength,　the　theoretical　formula　of　upper　bound　theorem　(τ)　for　adhesive　shear　strength　is　deduced.　Based　on　the　test　result,　the　main　parameter　in　the　formula　is　also　determine,　which　can　help　the　retrofit　design　of　concrete　structures　by　self-compacting　concrete.