A cascade linkage-cleavage switch-on system triggered by cupric ion was established.The substrate strand was labeled with a fluorescence and a corresponding quencher at the two ends,making the background low fluorescence intensity.The enzyme strand was splitted at proper position,and labeled with azide and alkyne in the two split enzyme strands at the split positon respectively.With the presence of Cu2+ ion and ascorbic acid,the two split catalytic strands would be ligated first to form an integrated enzyme strand,which process was also accelerated by the substrate template-directed effect.Then,with Cu2+ ion and ascorbic acid,the integrated enzyme strand would catalytic the substrate strand at specific guanine,and thus released the fluorescent signal to realize this cascade linkage-cleavage switch-on system work.The main strategy of this work is that through the click ligation of the two split enzyme strands,the integrated enzyme strand regains catalytic activity and thereby catalysis the substrate strand to cleave.