A gel bead having a code, a preparation method therefor, and an application thereof. At least two types of linkers are attached to the gel bead; the linkers are nucleotide chains, and each comprises a pairing region, a barcode region, and a primer region that are connected in sequence; the pairing region comprises a sequencing primer modified by Acrydite; the pairing region is modified by a photosensitive group. The gel bead having a code is prepared by microfluidic technology and two rounds of annealing and extension, and the synthesis method is simple; the linkers can be shed under the condition of exposure to ultraviolet, and then used as primers to amplify the open chromatin of a cell nucleus; moreover, the barcode regions on the linkers can be used as recognition sequences, and sequences having the same barcode regions are from a same cell; when performing high-throughput sequencing, sequencing results can be classified by barcode regions, and the obtained results are attributed to individual single cells, thereby achieving single-cell ATAC-seq.