Provided are an isolated oligonucleotide and a use thereof in nucleic acid sequencing, wherein the isolated oligonucleotide comprises a first strand, wherein the 5′-end nucleotide of the first strand has a phosphate group, and the 3′-end nucleotide of the first strand is a dideoxynucleotide, and a second strand, wherein the 5′-end nucleotide of the second strand does not have a phosphate group, and the 3′-end nucleotide of the second strand is a dideoxynucleotide, wherein the first strand is longer than the second strand in length, and a double-stranded structure is formed between the first strand and the second strand.