Objective To investigate the effect of type 2 diabetes mellitus on the prognosis of coronary heart disease patients who had a complication of heart failure with preserved ejection fraction. Metohds A retrospective study was performed with 393 coronary heart disease patients who were complicated with heart failure with preserved ejection fraction. The diagnosis was based on the results of echocardiography and coronary angiography at the heart center of the First Affiliated Hospital of Xinjiang Medical University assessed from January 2017 to December 2017. The patients were divided into diabetic group and non-diabetic group. The incidence of major adverse cardiovascular events (MACE) was compared between the two groups. In addition, the incidence of MACE was compared between the complete revascularization group and the incomplete revascularization group. Multivariate Cox regression analysis was used to analyze the effect of the risk factors on prognosis. Results The prevalence of hypertension and the use of ACEi/ARB in the diabetic group were higher than those in the non-diabetic group (P<0.05), and the level of high-density lipoprotein in the diabetic group was lower than that in the non-diabetic group (P<0.05). The incidence of MACE in the diabetic group (35.8%) was higher than that in non-diabetic group (25%, P=0.027). Complete revascularization improved the prognosis and reduced the incidence of MACE in both the diabetic group and non-diabetic group (P<0.05). Multivariate Cox regression analysis showed that a history of myocardial infarction (HR=0.44, 95%CI 0.20 to 1.00, P=0.049), incomplete revascularization (HR=17.28, 95%CI 2.34 to 127.43, P=0.005), and ejection fraction (HR=0.90, 95%CI 0.82 to 1.00, P=0.046) were associated with the occurrence of MACE in patients with coronary heart disease complicated with heart failure with preserved ejection fraction. Conclusion Type 2 diabetes mellitus affects the prognosis of coronary heart disease patients who have complication of heart failure with preserved ejection fraction. Complete revascularization can improve the prognosis of type 2 diabetic patients with coronary heart disease who have complications of heart failure with preserved ejection fraction.