Objective:To study the cognitive function of middle-age and old patients with type 2 diabetes mellitus(T2DM) and related factors. Methods:Questionnaires were used to investigate 155 patients with T2DM to study the cognitive function and the possible infected factors of memory and non-memory. Results:Cognitive function of the patients with T2DM was not only associated with age(r = -0.366),sex(r = -0.374),educational level(r = 0.574) and incomes(r = 0.268),but also with course of diabetes disease(r = -0.247),the levels of blood glucose(r = -0.269),HBA1C(r = -0.235) and systolic pressure(r = -0.280). The patients with T2DM combined hypertension displayed significant difference to the controls in calculating(P = 0.006) and repeating sentence(P = 0.006) in MMSE,the right numbers of point pictures(P = 0.001) and the expended time of point pictures(P = 0.016). Conclusion:The impairment of cognitive function of middle-age and old patients with T2DM was concerned with age,sex,educational level,incomes,and the levels of blood glucose,combined hypertension and the level of hypertension. Control the level of blood glucose and hypertension effectively should prevent and mitigate the deterioration of cognition of T2DM.