Method for repairing dna terminal end and adding a

Provided is a method for repairing a DNA terminal end and adding A, said method comprising: in the same reaction system, in the presence of dNTP, using a polymerase to blunt or flatten a fragmented DNA terminal end, and using a polynucleotide kinase to transform a 5'-hydroxyl into a 5'-phosphate group and transform a 3'-phosphate group into a 3'-hydroxyl; in the presence of excess dATP, using a polymerase not having exonucleolytic activity to add dATP to a double-stranded DNA 3' terminal end. Using the method, a DNA terminal end is repaired and A is added in the same reaction system, thus simplifying enzyme reaction and purification steps, increasing the efficiency of transforming starting DNA into ligatable adapter DNA, and reducing the requirement of the total amount of starting DNA.