Abnormal　expression　of　miRNAs　is　often　detected　in　various　human　cancers.　DNAzyme　machines　combined　with　gold　nanoparticles　(AuNPs)　hold　promise　for　detecting　specific　miRNAs　in　living　cells　but　show　short　circulation　time　due　to　the　fragility　of　catalytic　core.　Using　miRNA-21　as　the　model　target,　by　introducing　a　circular　bulging　DNA　shield　into　the　middle　of　the　catalytic　core,　we　report　herein　a　self-protected　DNAzyme　(E)　walker　capable　of　fully　stepping　on　the　substrate　(S)-modified　AuNP　for　imaging　intracellular　miRNAs.　The　DNAzyme　walker　exhibits　5-fold　enhanced　serum　resistance　and　more　than　8-fold　enhanced　catalytic　activity,　contributing　to　the　capability　to　image　miRNAs　much　higher　than　commercial　transfection　reagent　and　well-known　FISH　technique.　Diseased　cells　can　accurately　be　distinguished　from　healthy　cells.　Due　to　its　universality,　DNAzyme　walker　can　be　extended　for　imaging　other　miRNAs　only　by　changing　target　binding　domain,　indicating　a　promising　tool　for　cancer　diagnosis　and　prognosis.