Objective To explore the relationship between cognitive frailty, social isolation and cognitive reserve in elderly patients with type 2 diabetes mellitus, and to provide a reference for developing targeted intervention to delay the progression of cognitive decline in patients.Methods Six hundred and eight elderly patients with type 2 diabetes were conveniently selected, then they were investigated by using a general information questionnaire, the Frailty Scale, the Mini-Mental State Examination, the Lubben Social Network Scale-6, and the Cognitive Reserve Index questionnaire.Results The incidence of cognitive frailty in the participants was 27.0%, the incidence of social isolation was 31.3%, and the total score of cognitive reserve was 81.0（74.0,96.0） points.Correlation analysis showed that, cognitive frailty was negatively correlated with the risk of social isolation, and negatively correlated with cognitive reserve （all P＜0.05）; the risk of social isolation was positively correlated with cognitive reserve （P＜0.05） .The results of multivariate logistic regression analysis showed that, education, monthly income, the number of chronic diseases, polypharmacy, sleep duration at night, social isolation and cognitive reserve were the influencing factors of cognitive frailty in elderly patients with type 2 diabetes （all P＜0.05）.Conclusion The incidence of cognitive frailty and social isolation in the elderly patients with type 2 diabetes are high, and their incidence of cognitive reserve is low.The patients with higher risk of social isolation and lower cognitive reserve, are prone to have higher incidence of cognitive frailty.Healthcare professionals should pay attention to the social isolation and cognitive reserve status of elderly patients with type 2 diabetes and strengthen interventions to prevent their cognitive frailty.