Small　amount　of　lead　ions　(Pb2+)　can　cause　great　harm　to　human　health,　it　is　important　to　develop　some　simple　but　sensitive　methods　to　detect　Pb2+　quickly　and　accurately.　In　this　study,　a　sensitive　method　has　been　developed　for　Pb2+　detection　based　on　the　difference　of　gold　monomer　ratio　using　a　dark　field　microscope　(DFM)　as　readout　system.　The　proposed　method　employed　single-particle　gold　nanoparticles　(AuNPs)　and　8-17　DNAzyme　as　signal　converter　and　identification　unit,　respectively.　The　8-17　DNAzyme　consists　of　a　catalytic　strand　and　a　substrate　strand,　the　5　＇　end　of　the　two　strands　are　modified　with　sulfhydryl　groups.　The　8-17　DNAzyme　is　firmly　modified　on　the　surface　of　AuNPs　(50　nm,　AuNPs1)　in　advance,　in　the　absence　of　Pb2+,　AuNP　aggregation　is　occurred　by　adding　AuNPs　(20　nm,　AuNPs2)　as　they　can　interact　with　the　other　end　of　the　dsDNA.　In　the　presence　of　Pb2+,　due　to　the　specific　cleavage　of　the　substrate　chain　by　Pb2+,　another　-SH　leaves　away　from　AuNPs1,　the　aggregation　of　AuNPs　cannot　be　occurred.　AuNP　aggregates　can　be　easily　distinguished　from　the　monomers　under　DFM　because　the　aggregation　can　induce　green-to-yellow　scattering　color　changing,　and　the　monomer　ratio　summarized　by　Image　J　can　be　used　for　quantitative　analysis.　The　linear　response　range　is　0.1-100.0　pM　with　a　detection　limit　of　0.075　pM.　The　proposed　method　has　been　applied　to　detect　Pb2+　in　lake　water　and　human　blood　serum　samples　with　satisfied　results.