Diabetes is a chronic disease that affects many people, with both its incidence and prevalence rising globally. Diabetes can lead to various complications, among which cognitive impairment in diabetic patients significantly impacts their daily life and blood glucose management, complicating treatment and worsening prognosis. Therefore, the early diagnosis and treatment of cognitive impairment are essential to ensure the health of diabetic patients. However, there is currently no widely accepted and effective method for the early diagnosis of diabetes-related cognitive impairment. This review aims to summarize potential screening and diagnostic methods, as well as biomarkers, for cognitive impairment in diabetes, including retinal structure and function examination, brain imaging, and peripheral blood biomarkers, providing valuable information and support for clinical decision making and future research.