Abstract: The invention discloses a genetically engineered bacterium in which the gene encoding adenine deaminase on the genome of the bacterium is knocked out or/and the gene encoding the enzyme in the NAD+ anabolic pathway is integrated on the genome of the bacterium. The invention also discloses a construction method of the above-mentioned genetically engineered bacteria. The gene encoding adenine deaminase on the genome of the host strain is knocked out to obtain a strain with high NAD+ yield. Or the expression cassettes of the gene encoding the enzyme in the NAD+ synthesis pathway are constructed separately, and then the enzyme encoding The gene expression cassette is integrated into the genome of the host strain whose gene encoding adenine deaminase is knocked out to construct a strain with high NAD+ production. The application of the above genetically engineered bacteria is disclosed. A method of producing NAD+ is disclosed.