A　growing　number　of　studies　suggest　that　miRNAs　play　a　vital　role　in　the　diagnosis　and　treatment　of　several　diseases,　especially　for　cancers.　However,　miRNA　detection　still　remains　great　challenges　because　of　its　small　size,　low　abundance　and　easy　degradation.　In　this　contribution,　we　demonstrate　an　intelligent　DNA　machine　for　the　detection　of　miRNA-21　via　designing　a　multiple　palindrome-mediated　strand　displacement　amplification　(called　MPSDA)　strategy　combined　with　fluorescence　measurement.　Essentially,　the　nano-machine　is　a　scarecrow　-shaped　DNA　nanoprobe　(S-nanoprobe)　assembled　from　only　three　single-stranded　DNAs　(ssDNAs)　each　with　a　palindromic　fragment　at　the　3　＇-end.　In　the　presence　of　target,　S-nanoprobe　can　be　dissembled　into　two　parts,　leading　to　the　release　of　palindromic　ends　that　can　execute　MPSDA　under　DNA　polymerase.　Benefiting　from　the　high　efficiency　of　MPSDA,　S-nanoprobe　can　be　used　to　detect　down　to　1　fM　of　target　and　exhibit　a　high　specificity.　Target　miRNA　can　be　100%　discriminated　from　homologous　miRNAs　and　can　also　be　sensitively　detected　in　complex　biological　samples.　More　excitingly,　a　high　recovery　rate,　desirable　blind　test　results　and　precise　target　assay　in　real　samples　demonstrate　the　huge　application　potential　of　S-nanoprobe　in　the　detection　of　tumor　-associated　biomarkers　in　early　diagnosis.