The subgingival plaque of patients with periodontal disease contains a large number of pathogenic bacteria and is a reservoir of oral pathogenic bacteria, especially Helicobacter pylori and respiratory pathogens. Diabetic patients are more prone to periodontitis, and a thorough periodontal treatment in diabetic patients with periodontitis will reduce the incidence of periodontal disease. Generally, when we talk about periodontal disease at its most serious, it will jeopardize the loosening of the teeth around that bad tooth, and the cure for periodontal disease will not be too good, so that tooth can only be extracted. Therefore, diabetes and periodontal disease are risk factors for each other. Poorly controlled blood sugar makes it difficult to ensure periodontal health, and conversely, uncontrolled periodontal inflammation makes it difficult to achieve normal blood sugar levels. The pathological mechanism of diabetes mellitus with periodontal disease may be defective leukocyte chemotaxis and phagocytosis, altered vascular basement membranes in tissues, reduced collagen synthesis, reduced bone matrix formation, and decreased immune regulation, leaving patients with reduced resistance to infection and impaired wound healing. Diabetes has a significant impact on the vascular system, inflammatory response and tissue repair, thus altering the individual’s response to plaque bacteria, affecting the clinical manifestations of periodontal disease, the pathological process and the response to periodontal treatment. On the other hand, diabetic patients with severe periodontitis have much less glycemic control than those without periodontitis. Thorough and effective periodontal treatment not only leads to the reduction of periodontal lesions, but also leads to a significant reduction of glycated hemoglobin levels in diabetic patients and reduces insulin resistance in patients with severe diabetes, thus improving glycemic control and the patient’s condition. Therefore, the prevention and treatment of periodontal disease is an important part of controlling diabetes. In conclusion, diabetic patients must monitor blood glucose diligently, and actively pursue systematic and standardized treatment of periodontal disease based on blood glucose control and anti-inflammation.