Double-stranded nucleic acid cyclization method, methylation sequencing library construction method and kit

The invention discloses a nucleic acid double-chain cyclization method, a methylation sequencing library construction method and a kit. The nucleic acid double-strand cyclization method comprises the following steps: providing a forward primer and a reverse primer, wherein each of the forward primer and the reverse primer comprises a U basic group, the nucleotide number difference of the upstream sequences of the 5'ends of the U basic groups of the forward primer and the reverse primer is N, and the upstream sequences of the 5 'ends of the U basic groups of the forward primer and the reverse primer are at least partially and reversely complementary; amplifying the nucleic acid fragment by using the primer pair to obtain an amplification product; a USER enzyme is used for cutting off U basic groups in the amplification product, then a mononucleotide gap is formed, chain dissociation occurs to the residual nucleotide sequence from the gap to the 5'end due to the unstable structure, and then partially complement