A　novel　colorimetric　switch　based　on　the　copper(I)-catalyzed　azide-alkyne　cycloaddition　(CuAAC)　reaction　has　been　developed.　G-quadruplex-hemin　DNAzyme　catalyzes　the　oxidation　of　2,2＇-azinobis(3-ethylbenzothiozoline)-6-sulfonic　acid　(ABTS)　to　form　ABTS(+),　the　UV　absorbance　of　the　solution　increased　greatly　and　the　color　of　the　solution　changed　to　dark　green.　However,　in　the　presence　of　an　azide　complex,　the　absorbance　signal　decreased　and　the　solution　became　light　green　since　the　catalytic　ability　of　the　hemin　was　inhibited　by　the　azide　groups.　However,　once　propargylamine　has　been　added　into　the　above　reaction　system,　which　would　react　with　azide　groups　through　the　CuAAC　reaction,　the　solution　becomes　dark　green　again　and　the　absorption　intensity　of　the　system　is　also　increased.　The　proposed　switch　allows　a　good　reversibility　and　can　be　identified　clearly　by　the　naked　eye.　In　addition,　the　method　has　been　applied　to　detect　some　pesticides,　which　have　alkynyl　groups　(flumioxazin),　with　high　sensitivity　and　selectivity,　where　the　UV　absorbance　has　a　direct　linear　relationship　with　the　logarithm　of　flumioxazin　concentrations　in　the　range　of　0.14-14　nM,　and　the　limit　of　detection　was　0.056　nM　(S/N　=　3),　which　can　meet　the　requirement　of　the　maximum　residue　limits　(MRLs)　of　United　States　of　America　(56　nM).