MicroRNAs　(miRNAs)　have　been　identified　as　important　biomarkers　with　great　significance　for　diagnosis　and　treatment　of　various　diseases.　However,　their　unique　properties,　such　as　small　size,　high　sequence　homology,　and　low　abundance,　make　quantitative　analysis　of　miRNAs　extremely　challenging.　Herein,　we　reported　a　cascade　catalytic　hairpin　assembly　(CCHA)　for　sensitive　and　selective　detection　of　miRNA　with　three　kinds　of　hairpin　probes　(HP1,　HP2,　and　HP3).　In　the　presence　of　target　miRNA,　a　series　of　toehold-mediated　intermolecular　DNA　strand　displacement　and　hybridization　was　activated　among　HP1,　HP2,　and　HP3　to　assembly　numbers　of　DNA　nanoobjects.　During　this　period,　the　fluorescence　response　was　greatly　intensified　to　indicate　the　presence　and　expression　level　of　interested　target　miRNA.　We　have　demonstrated　that　the　proposed　method　exhibits　a　high　assay　sensitivity　to　detect　low　concentration　target　and　an　excellent　sequence　specificity　to　distinguish　even　a　single-nucleotide　difference　in　vitro.　Moreover,　we　also　demonstrated　that　our　design　enables　the　intracellular　imaging　of　miRNA　in　live　cancer　and　normal　cells.　These　results　showing　the　promising　potential　of　our　CCHA　for　powerful　biosensing,　clinic　diagnosis,　or　prognosis.