<p>Provided are DNA tags for constructing a MeDIP-seq library, a MeDIP-seq library and a method for preparing the same, detection method for the methylation of a plurality of DNA samples, and a kit for constructing the MeDIP-seq library. The DNA tags consist of the nucleotides shown in SEQ ID NO: (3N-2), in which N is any integer from 1 to 20.</p>