The invention belongs to the field of aquatic animal gene engineering and relates to a CpG ODN sequence with grass carp immune enhancement activity and a use thereof. The CpG ODN sequence with grass carp immune enhancement activity is a nucleotide sequence shown in the formula of SEQ ID NO: 1 and is a CpG motif-containing oligodeoxynucleotide sequence containing three sequences of AACGTT and one palindromic sequence of TCGA. Through preliminary screening of grass carp head-kidney mononuclear cells and a grass carp kidney cell line, it is verified that CpG improves grass carp immune activity. Through CpG activation on a signal path related gene, a CpG ODN sequence with the strongest immune enhancement activity to grass carp cells is selected. A virus attacking test proves that the CpG ODN sequence has a strong immune enhancement effect. The CpG ODN sequence can be processed to form a grass carp immunopotentiator, immunoadjuvant or vaccine and can be promoted and used in prevention of grass carp diseases.