Abstract: In order to study the key genes that affect the post-acidification of Lactobacillus bulgaricus, it provides a theoretical basis for the development of yogurt starter at the molecular level. In this experiment, 8 existing Lactobacillus bulgaricus in the laboratory were used as starting strains. Based on their growth performance and acid sensitivity, 4 strains of Lactobacillus bulgaricus(KLDS1.0207, KLDS1.0205, KLDS1.1001, and KLDS1.1011) with obvious differences in acid production were selected. Four strains of Lactobacillus bulgaricus were tested for the curd time, titrated acidity, and lactose consumption of four strains of Lactobacillus bulgaricus single strains. The analysis showed that the strain KLDS1.1011 had the weakest acidification capacity.Genome sequencing of strain KLDS1.1011 via Illumina HiSeq and Illumina MiSeq sequencing platform. The total length of the KLDS1.1011 genome was 1884491 bp.The average G+C content was 39.83%. A total of 2098 CDS were predicted in the genome, with a total length of 1622760 bp.The total length of the coding region accounted for 85.97% of the whole genome and the average length of the coding gene was 773 bp. The genomes of Lactobacillus bulgaricus KLDS1.1011 and KLDS1.0207 were used homology cluster analysis to compare. It was found that there were 1631 genes in common, KLDS1.1011 had 353 unique genes, and KLDS1.0207 had 320 unique genes. Furthermore, by annotating the KEGG pathway and analyzing the post-acidification related pathways of the unique genes, 6 genes related to post-acidification were obtained. The four genes 1011_GM000805, 1.1011_GM002068, 1.1011_GM000803, and 1.1011_GM000804 were related to the formation of biofilms and the material transport of strains. 1.1011_GM000260 gene belonged to the pyruvate metabolism pathway and was an important pathway in the lactic acid production process and the 1.1011_GM000194 gene was a key enzyme gene for proteolysis. It would provide an important theoretical basis for the weak post-acidification characteristics of strain KLDS1.1011 at the gene level.