A CpG DNA adjuvant in avian vaccines is disclosed, which includes an immuno-stimulatory oligodeoxynucleotide (ODN) having a plurality of TCG tandem repeats at a 5' end, a poly-G structure at a 3' end, and at least one unmethylated CpG motif with avian specific flanking sequences at two ends thereof between the 5' end and the 3' end. The CpG DNA adjuvant in avian vaccines is advantageous for large-scale production; specifically enhanced avian innate and adaptive immune responses, and the CpG DNA adjuvant is difficult to be digested by DNase due to its particular structures.